RECORD: Darwin, C. R. Geological diary: Falkland Islands. [1834-] CUL-DAR33.166-216 Transcribed by Kees Rookmaaker, edited by John van Wyhe (Darwin Online, http://darwin-online.org.uk/)
REVISION HISTORY: Transcribed from the microfilm by Kees Rookmaaker, corrections and editing against the manuscript by John van Wyhe 7.2010. RN3
NOTE: This document, part of the largest scientific document composed by Darwin during the voyage of the Beagle, is written mostly in ink. Marginal notes are here integrated into the text.
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Reproduced with the permission of the Syndics of Cambridge University Library and William Huxley Darwin.
See the introduction to the Geological Diary by Gordon Chancellor.
Slate & Sandstone
extensive low country intersected by arms from St. ??
45° 30° 40°
10° 45 40°
Great valley of fragments
Hill 962 ft
Valley of fragments
N.B. Generally. where dips are opposite small lateral dip might also be moved in the cross valleys: but I have only put them down where best seen. —
Main range 1400 ft?
Further in this direction. hills turn up in NW by W lines & quartz dips to SW by S. 40°
pencil and ink sketch, with blue watercolour.
[Drawn on thin tracing paper that is backed with card. These are separate slips although they were microfilmed together. The sketch is in black ink. The versos of the cards are blank.]
NB: This not an exact representation of nature, only an illustration.
[Drawn on thin tracing paper that is backed with card.]
A 960 ft
C 700 ft
Fig: 7. [sketch in black ink on thick cream-coloured paper, verso is blank, no watermarks]
Section of the great central range
useless] both instances in pencil.
My observations on the geology of the Falkland Islands were
made during two visits to the Eastern Isle
in the Beagle, in the months
of March 1833 & 1834. At the latter of these periods I crossed from Berkle Berkeley's Sound, to Choiseul bay & returned by a longer circuit. From
a series of specimens which, Mr Kent, when in the Adventure, had
the kindness to collect for me at the Western island. I feel assured that
the structure & geology of the whole group is of a very uniform nature.
The Falkland Islands cover a space of 130 miles of Longitude by 60 of Latitude;
which may be compared to the dimensions of the Isd of — Sardinia. The land
is much intersected by numerous winding arms from the sea: with the exception
of a few naked ridges of naked grey rock, which never attain any great
elevation, the whole surface is covered by a peaty soil bearing a brown withered
[in margin] Mr Austin in a paper read to Sedg. Soc. says that no shells in clay-slate owing change superinduced by cleavage undermining sandstone full of shells S. [Devon]
now first describe the geology of the Eastern
Island & particularly of the part in the neighbourhood of Berkeley's
Sound. A little way inland. on the South side of this deep bay, is situated
the central chain or axis of the Island; — it runs about E & W, has
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a mean height of about 1500 ft & consists of Quartz Rock. On the same side of the bay & likewise on the northern shore, there are several lower & parallel ridges of a similar constitution.
The intervening low country is entirely composed of Clay Slates & sandstone. Although the mineralogical nature of the rocks is
simple & but a little varied, we shall soon see that their structure is highly complicated: on this latter subject, the facts appear to me, very interesting & worthy of attention. —
To begin with the low country: The clay-slates are generally
of a pale brown color & sometimes blue 1082 1083; the stone is rather
soft; in one locality there was a harder kind of a black color & containing
scales of mica. 1085 The slate is much laminated, the layers have their surfaces
slightly undulating but quite smooth, but not quite even,
slightly undulating. Cleavage Whereever I examined the cleavage, I found the
laminae directed with few exceptions from (W or W by N) to (E or E by S);
the angle of inclination was great, generally more than 50°, up to vertical;
the dip varied towards was either N or S., the latter perhaps being
rather more frequent. —
cleavage] added pencil in margin.
there are a few pencil insertions on this page
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The sandstone is in smaller quantity & is also subordinate to the clay slate; it is fine grained, of a pale yellowish color & moderately hard; it is frequently banded with narrow stripes or slight alterations in color. The sandstone not infrequently becomes slate in which case it contains scales of mica.
This rock is chiefly remarkable.
by the for very numerous impressions of organic remains.
1089 ... 1128 1152 1903 ... 09 1939 ... 1946
These are chiefly species of the subgenera ?
of the Terebratulae & of Entrochites; of the latter I only found procured the joints of the stems, but I heard of one flower=like head having been found. In one part there were numerous casts of what which appeared to have been formed by some coral, such as Gorgonia; even to this day some fibres of organic matter (a) yet remain in the tubular cavities. These casts occur in particular seams in the sandstone & sometimes in such quantity, that the rock is wholly composed of them. The cementing matter frequently instead of being a sandstone, is frequently changed into a compact hard blue siliceous clay slate.
I could not perceive any trace of calcareous matter in the casts, or in the imbedding rocks. —
there are a few pencil insertions on this page
Do not the Entrochites & other organic remains. indicate a climate previously warmer? when the latitude of the place in 51 degrees in the Southern hemisphere is considered even a remote probability on such a point becomes interesting. —
The strata of sandstone vary in thickness from two or three inches to as many feet; in one place there was an extensive bed, upwards of 12 ft thick. In the neighbourhood of Berkeley's Sound these strata generally both rest on & are covered by, the ordinary clay slate, the laminae of which are vertical or highly inclines & run in their usual direction.
With respect to It is easy to ascertain the stratification
of any mass of sandstone, it is of easy & certain ascertainment:
the seams of organic remains are being parallel to the surfaces of
the beds & from the flatness of the shells it is manifest they would show
the original plane of deposition.
The stratification is generally subject to much irregularity;
but from the greater number of
instances observations, the more usual
inclination is at an angle from 10° to 20° to between S & SW, in some
places however the beds were horizontal, then much twisted, again dipping
at a higher angle to the northward, occasionally even to such points
as W by S. or SSE. — At the a section, when a one sandstone
stratum was most clearly seen, lying between masses of clay slate, the latter
rock had its
stratification] pencil in margin.
there are a few pencil insertions on this page
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laminae vertical & striking in the usual direction W by 1/2 N. & E by 1/2 S. whilst the sandstone stratum was inclined at 14° to W by S.
which this being rather an unusual point of dip. Here then is affording an excellent instance, by which it can be proved that where the position of the laminae clay-slate is by no means was not directly connected with the plane of deposition. When The imbedded sandstone, in those parts where organic remains are not abundant, is when struck it frequently splinters, at right angles to the stripes & natural planes of divisions. splinter at ∠ angles: this kind of fracture, is contrary to what would have been expected from the appearance of the stone, & it often rendered the extraction of the fossils difficult.
I am inclined to attribute this circumstance to the
same cause, which has given to the surrounding slate its vertical cleavage.
I may mention as a proof of the extreme difficulty in ascertaining the stratification
of clay slate, that in a low cliff. there were smooth (2), numerous (1) equidistant
planes of division, (in addition to the ordinary cleavage) which dipped at
splinter at ∠ angles] added pencil in margin.
there are a few pencil insertions on this page
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angle of 35°. to NW by N; at the time of first meeting
with these fissures, I did not know of the sandstone & therefore imagined
they were true strata. — I nowhere could I did observed any sort
of traces lines of division in the clay strata, or any changes of constitution,
or even differences of color. in planes. parallel to those, which are known
to be the original ones of subaqueous depositions indicative of stratification.
In one place alone, I observed two or three imperfect shells 1129 ... 1131
within the laminae of clay slate; & generally during the formation of
that rock it cd seem that circumstances were unfavourable. either
to the growth or the subsequent preservation of marine animals
remains: It is evident from the thickness of the seams. composed of large
shells, that considerable intervals of time must have elapsed between the
successive deposits of clay slate. —
In a valley between the main central quartz range & a smaller one to the North of it, I observed the following fact: In an extent of some hundred yards there is found a common blue slate, with the usual strike of N by 1/2 W & dipping at an angle between 50° & 60°; within the laminae
there are a several pencil insertions on this page
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of clay slate there are included numerous parallel layers of a
sandstone precisely similar, in every respect possible, excepting in being
finer grained & in not containing organic remains, to the fossiliferous
strata at the settlement above described; the layers are of various thickness,
they & had exactly the same exact (necessarily so, from being
parallel) dip with the slate. 3) In a vertical direction, 1) I could not
see, 5) owing to the lowness of the cliff, 2) the sandstone for more than
ten or twenty feet. Any one who had happening happened to see this
section alone, & without considering any other facts, would have
been convinced, that the even parallel layers of slate & sandstone
had been once horizontally deposited & were now has then
tilted up, from by a force from below into their present highly inclined
position. On a close examination however, at parts where a considerable thickness
of the sandstone beds. was exposed, waving irregular ferruginous water-lines,
might be seen traversing 2) in a nearly horizontal direction, 1) the inclined
layers. — Another line of coast, on one of the arms of Berkeley Sound, showed
there are a several pencil insertions on this page
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similar, but still more curious appearances (3)
Also In one place the same kinds as 2) as those already described, 1) of slate & sandstone, in the first place, occurred in highly inclined parallel layers, running in their usual direction W by N & E by S; secondly, only in another at a short distance apart from former were irregular horizontal beds of sandstone between were covered from above & below by in the same vertically laminated slate: Vide Fig. 1 and lately, in more than one section, I saw the extremities of these highly inclined layers of sandstone, bending at their lower extremities, & joining on to the & then becoming horizontal; — or it might be described, that the horizontal sandstone thinned out, & the extremities of the beds were caught up between the inclined layers of slate. —
The laminated clay-slate has been repeatedly shown to occur both
below beneath strata of sandstone, which retain a direction,
nearly horizontal; hence we must infer that the layers of slate have not been
upheaved from a less inclined into their present position. And because the
slate, which includes the layers of sandstone, has a direction & inclination
the same, as when it occurs by itself,
Fig. 1] ink over pencil.
there are a several pencil insertions on this page
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we must grant, that the sandstone layers also have not been upheaved.
This proof however is rendered almost unnecessary, by the very curious fact
of the extremities of the irregular horizontal beds of sandstone, running
up between the laminae of the slate. (a) omitted (a)
We must them come
to the conclusion May we not therefore suspect, that the same power, which
has given 2) to the rocks. over a large district 1) a laminated structure,
directed in a particular manner, has also been capable during the of
separating the ingredients of slates & sandstones & placing them in
layers inclined at the usual angle. — I have said, that the true strata, although
subject to much irregularity, most generally are inclined to a point,
between S & SW; now as the laminae of slate strike W by N & E by S
& as they are seem to exert some a tendency to entangle the sandstone,
the cause of that dip (which is not great) & of the irregularities, would
appear to lie, in a struggle maintained between ordinary horizontal deposition
& the power which has effected the cleavage structure of the slates. —
(b) omitted (b)
there are a few pencil insertions on this page. This folio bears a watermark "WILMOT 1834".
(a) moreover, it is evident that ordinary aqueous deposition, unaided by other powers,
appears is quite incapable of forming these nearly vertical layers. which possess an even thickness & so high an inclination
(b) It must also be remarked, that as it is improbable in the highest degree that all the strata should be consolidated at any one instant, so the impressement of the fissile structure, although directed in the same precise line, must be a successive action.
there are a few pencil insertions on this page
We now come to the description of the quartz rock, 2) of this
substance, 1) the hills, which rise out of the lower strata & sandstone
district, are all ! (I believe 3) without any exception, composed. — The quartz
rock, 1136 when in its purest state, is white, highly crystalline & formed
of rather coarse grains; a more common variety contains in its interstices,
small portions of a white powder, which possesses a strong aluminous smell
1078: 79; but is [3 words illeg] this substance, varies much in quantity,
when abundant, it gives rise to a singular mountain rock. In one place the
quartz being in smaller grains 1084
assumed assumes, an arenaceous
[West] 3d appearance; in another part, besides
the aluminous powder, there were are minute, black. imperfectly crystallized
specks of a mineral 1133. which appeared to be mica. These specks were arranged
in planes & gave to the rock a slightly laminated structure: taking
viewing the white powder in the place of as the original of a Feldspar,
I imagined I here saw an abortive attempt to form gneiss. Within one of the
quartz ranges, there was a quantity of rock, which very closely resembled
in structure a Breccia 1080; it consisted of angular & rounded
pieces of quartz 1134 imbedded in a compact hard white base. — I do not suppose
it is an ordinary breccia, but rather, that the aluminous
there are a several pencil insertions on this page
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substance, which generally occurs in the interstices, has been
united with some of the siliceous, to form the opake. white base, whilst the
remaining quartzose matter assumed a concretionary but angular structure;
in ordinary subaqueous deposits, such a process has taken places, as well
2) at a future period. 1) be mentioned in the geological account of King George's
With the exception of the central chain, the greater
number of quartz ridges are only elevated from two to five hundred feet above
the sea; such ridges almost compose almost compose the whole country of towards
the eastern extremity of the Island & especially on the northern side
of Berkley's sound. —
Strata of quartz
The quartz rock is divided into strata, which generally have a thickness. varying from less than one to even to three feet. The most usual line of strike is within a point on either side of W & E; the inclination being between the angles 30° & 45°. — On the northern side of Berkeley's Sound, all the beds dip a little to the westward of south, the basset edges of the various parallel ridges being presented to the opposite point. On the southern side of the Bay, the dip is either towards the
one or other side; but from some
irregularities north or south, but the strike is generally
Strata of quartz] added pencil in margin.
there are a few pencil insertions on this page. Several words in pencil and ink have been erased.
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[has a strike probably S]
in the line of hills, the strike is then sometimes W
by S & even sometimes WSW. Any very exact ascertainment of the position
of the quartz strata is difficult from a trifling quâquâ versal dip, which
occurs in several points in the line of ridges; this subject will presently
be mentioned in detail.
The strike of the laminae of slate & strata of quartz is generally
the same, but in the inclination there is this remarkable difference, that
in the slate the angle as rarely falls below. as in the quartz it exceeds
forty five degrees. The same
line W by N & E by S general situation
is common also to the bearing of the principal, as well as subordinate
ridges of quartz; hence the form of land & outline of the shores is influenced
to a certain extent by this fact circumstance. With the exception of
the central chain, the greater number of hills, do not commonly rise more
than from two to five hundred feet above the sea; of such ridges almost
compose the whole country towards the Eastern extremity of the Island &
especially on the Northern side of Berkeley's Sound. — With respect to the
connection of the quartz & slate formations. I was not fortunate enough
to meet with any direct case of superposition. But in several places
[has a strike probably S] very faint pencil.
circumstance] pencil insertion.
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by following the course of the beaches. I traced by a prolonged
& most gradual change, the quartz passing into clay slate. Rocks intermediate
between in character between these two are of common occurrence. As
the fact of an insensible change from strata of pure quartz white crystalline
Quartz to a laminated clay slate, appeared to be very strange, I strictly
examined during both visits a part of the coast at Johnson's harbor, where
the following order of rocks was observed. The space described is about half
a mile & the direction of the shores oblique, but not at a large angle,
to the usual line of strike. (1st) (a) We have the regular white
crystalline granular quartz 1895a, with the aluminous particles in the interstices;
(2nd) this gradually passes into a slightly ferruginous brown stone,
which [ illeg] breaks with more of an aranaceous ((siliceous
sandstone)) 1893 like & less of a crystalline fracture, & is not so
hard; sometimes it contains a little mica. (3d) The quartz reassumes
its pure character & (4th) then again. as before, loses it.
— (5th) By very insensible changes, the stone becomes finer &
finer in grain, its fracture more earthy, till, after partial oscillations
in purity we have a rock. which may almost be called a siliceous sand slate.
((siliceous sandstone))] pencil insertion.
siliceous sand] pencil insertion.
(a) I have placed the numbers of the specimens by the side in proper order: the expression "like" means. that that fragment did not come from the very spot, but that the rock was there as similar as to render it superfluous to bring away any more. —
(6th) A few seams of a compact blue slate are included. 1897 (7th) It becomes converted into a greenish, rather coarse but true clay-slate. I have marked these seven stages, as so many distinct steps, but it must be remembered that such is not really the case; the changes with some trifling oscillations always being gradual. — Having passed over a beach of a couple of miles in length during all which space the same greenish slate, or the (7th) step, was continued, we again come to one of those quartzose rocks of an intermediate character: this soon became pure & then rather suddenly in the space of 20 yards was succeeded by the ordinary pale colored clay slate. (a) The structure in all the intermediate rocks is obscure, the numerous planes of division are not well developed & cross each other in many directions. The beds of pure quartz, where last distinguishable, were directed in the usual line, but dipped at a small angle to NNE. which point, on this side of Berkleys sound, is uncommon; the laminae of slate. where first well developed, were inclined at an angle of 65° to the almost invariable point S. by W. Here then the transition in composition,
(a) the specimens. collected during my first visit to this spot, show the quartz becoming earthy & ferruginous (1081). & then intermediate of which state (1135) was as good a specimen. as could be found. — then imperfect state (1082) & lastly perfect (1083). —
& structure is perfect. — In another part of Berkeleys Sound,
to the settlement, I found the ferruginous earthy quartz rock,
described as intermediate in character, first alternating several times, in
nearly horizontal beds, with a coarse blue slate, & then insensibly passing
into it. At a short distance, the same stone gradually changed itself,
into a sandstone, precisely similar to that which contains the organic remains;
indeed & in one spot, although there it did not there possessing
posses the intire complete character of a sandstone, it contained an
obscure impression of a shell. It was very curious to behold observe
that no sooner, was, the passage completed, & the rock a true sandstone,
than it became subject to a laminated structure; although the surrounding
rocks possessed an irregular amorphous structure, yet here, the laminae were
much smoother & more regular, than as they commonly occur; & were
directed with a nearly vertical inclination to in the usual (W by N)
& (E by S) line. In many parts of the country, the intermediate rocks
were found, & not far distant
there are a few pencil insertions on this page
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the perfect quartz & slate, yet from the concealed state
of the surface, I did not notice any other section of consequence. — I may
mention an observation, but of the accuracy of which I do not feel, at all,
viz namely that the quartz rock contains the aluminous powder,
most abundantly, where it approaches near to the line of transition,
& therefore that the pure quartz rock is chiefly confined to the central
parts of the ranges. If this is the case, the change from the pure quartz
to the slate is indeed most gradual.
strata not rippled
I will not describe as a very irregular section crossing in a NNE & SSW line, the Eastern end of the island; the facts almost exclusively refer to the stratification of the quartz.
On the north side of Berkeleys sound, numerous & nearly
parallel ridges. as has already been said, all dip, at a general angle of
40° say below 30 &,
to a little to the westward of South.
crossing near head of Berkeley Sound
Berkeley Sound is a large piece of water, extending in a WNW line, about fifteen miles inland, its shores in the upper parts, are fringed, with slates. sandstone & the less crystalline or impure quartz rocks. —
strata not rippled] added pencil in margin.
crossing near head of Berkeley Sound] added pencil in margin.
say below 30 &] pencil insertion.
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Having crossed over a flat tract of such formations, we arrive at an E & W range of quartz hills, the strata of which, present, as before, their basset edges, to the North. The structure of one part of this ridge. is very remarkable; a convex hillock (a) is formed by curved strata, which dip away on all sides. The description will be rendered more clear, if we imagine in a line of elevation crossing yielding pliant strata, that a small definite portion could be raised a trifle above the general level; the effect would be to form a low oval mound entirely constructed of folding & concentric layers. Such is the structure of this spot; & if the mound had remained unbroken, the surface would have shown a smooth arched dome. One end however. has not only been broken off. but is slightly hollowed out; hence ascending by that point, the fractured ends of the successive strata. form so many inclined steps; &
on each the staircase, on each kind, is, in parts, flanked by a wall, the stones of which dipped away in opposite directions. — The scenes on a small scale presented a curious exhibition of natural architecture. the summit of the mound, from the strata, being horizontal,
(a) Hill of ruins of Pernetty?1
1 Pernety 1770.
was nearly flat & about one hundred yards wide. — From the "oval of elevation", if such an expression may be used, the strata declined on every side: choosing four points, the extent of lines at right angles to each other and where the structure could be best seen, I found that on the north side of the mound, the dip was at an angle of 28° to the north, — on the East side to E N E angle 14° — on South side to S by W. angle 29°, — on West side to W by N angle 16°. —
These inclined & folding strata
were joined by a
gradual curve to the horizontal ones of the summit. The layers of the quartz
rock have been much fractured & are divided by wide fissures: I noticed
also. that the convex surface of the arched parts are every where traversed
by innumerable thread-like veins of quartz, which generally formed a net-work,
the lines crossing each other at right angles.This fact will 2) in another
instance 1) be more fully described. The oval mound is situated in the higher
parts of a range of hills, which extend in a W & E line; the longer axis
however of the hillock itself, is directed
the extent of lines] pencil insertion.
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WNW & ESE; it is separated from the surrounding parts by two small transverse valleys filled with fragments of the quartz rock. the range has been described as constructed of strata, presenting their basset edges to the North; their inclination, in places distant several miles from each other, about equalled half a right angle; but immediately below, & rather more than, three hundred yards distant from, the mound with the quâquâ versal dip. the inclination amounted only to five degrees. On the South side of the range the strata,
the dipped with a varying angle towards the hills or to the North; therefore one or perhaps more synclinal lines are included within the range. —
Crossing a valley, about half a mile wide we come to a second & shorter range, which runs W by S & E by N. & parallel to the principal or central line of hills. The first range is directed W & E; hence these various chains have a tendency to approximate towards the eastern extremity of the islands.
The valley which separates, the first & second line, is very remarkable from a mass, which in truth
a few ink passages on this page have been erased and replaced with new writing in a lighter ink.
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may be called enormous, of angular fragments of quartz rock. It is probable, that some ridge of hills has here been quite overwhelmed and obliterated: the subject of the great fragments will presently be described at large. In this second range, the principal hill is 960 feet high. (Barom: observ:), it presents on its northern & southern slopes regular anticlinal strata;
vertical axis plain
the rocks on the summit, have suffered from extreme violence & hence perhaps it is, that we can there find scarcely any curvilinear beds.
Proceeding westward along the line of the same ridge, I will describe the several parts which are met with: first, at the south-western base of the 960 ft hill, there is a mass of strata dipping at 70° to S by W.
Beyond this, there is a low flat hill, the strata on the broad summit are horizontal, but those on the northern slope dip N by W angle 47°. & those on the Southern to the opposite point. Again a transverse valley separates this hill from another & higher one, the elevation of which is probably 700 feet. At its south-eastern foot, there are strata dipping at an angle of 60° to SSE, the
vertical axis plain] added pencil in margin.
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broken summits of which are curiously folded back on themselves (see fig: 2) Vide Fig. 2, & it is easy to trace in imagination the figure of the mass, when they were complete. It is probable in the case, before mentioned of the strata with the 70° dip, which are situated with respect to the line of hills, in a similar position, that they were at one time terminated by some such curvature; a small neighbouring gorge filled with great fragments probably owes its present state to these ruins.
The summit of the 700 feet hill, is composed of several crests the strata of which dip very regularly at angles 50°-55° to N by E or NNE. Some of the central strata, had their base extremities a very little curved over towards the South (see fig: 3). Fig: 3 Although the general stratification is inclined either towards the South or North, yet on the sides of the hills in the direction of the range, a tendency to a quaqua versal1 dip might be distinguished.
The rocks on the summit have in all cases been much shattered; in this hill, some of the fragments particularly attracted my attention. Close beneath the arched extremities, there was
1 A domed structure with the strata dipping away in all directions from a centre.
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lying, close to many fragments & apparently but little removed from its original position, an elongated block. Its transverse section was quadrant shaped, Fig. 4 two sides being at right angles to each other & the third curved; its length was about twelve feet & that of the base, or one of the radii six feet & nine inches. The surface of the arc is extremely smooth & regular:
I ought however rather to say of the
arched curved line, for it is not part of any mathematical figure, but perhaps most closely resembles the summit of a parabola (؟). Within the block, obscure lines of division, concentric with the arched surface, imperfectly form thick & highly curved strata. The block is transversed by one large & other smaller open fissures; these have partially destroyed the symmetry of the curvature, but that very want of continuity, shows on the first glance that they are owing to subsequent accident & that originally the fragment with ninety degrees (calling, T. fig: 4. the centre of an imperfect circle) of curvature was intire.
On close inspection the convex surfaces of these strata will be seen to be traversed at intervals of half an inch to two inches by thin veins, which vary in breadth from a tenth to the twentieth of an inch. They are not compact, but only partially filled up with crystallized quartz, the imperfect
close to many fragments] pencil insertion.
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crystalls being placed transversely to the walls of little fissure. the intermediate rock is quite solid & compact. These quartzose threads after extending in a straight line for a space, thin out towards each extremity, & when this happens, another vein either a little above or below, takes its origin & runs parallel to the extinct one. The greater number traverse the rocks in the direction of the axis of the archway or main curvature; but there are other veins. though fewer in number, which are placed at right angles to the first system & so form a network. I examined many fragments of curved strata & I found, the thread-like veins to occur in all. doom-shaped hill The connection between the strata being much arched & the presence of potentially solid veins is palpable;
in the direction of chief curvature & therefore of chief
extension of the convex parts, the greater number of veins are found, those
which are directed at right angles to the first lines, must originate, from
the fact, that each hill in the common ridge, has
been, to a cer
limited extent been a point of elevation; & therefore, that there is a
curvature in two directions.
It is impossible not to reflect with surprise, that at the period, when the strata were bent & doubled,
doom-shaped hill] pencil insertion.
Sulivan]] added pencil in margin.
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the now solid rock must have been nearly fluid.
The consistence was perhaps like that of honey mixed with flour, in which, if thick enough, a movement might cause small cracks. In the case of the quartz, either the superincumbent pressure caused the siliceous matter to be secreted from the surrounding semi-fluid stone or more probably the threads of pasty matter, drawn from side to side of the fissures assumed a crystalline structure & so gave rise to an appearance of subsequent infiltration.
The summits of all the hills, where the curved strata frequently occur present a scene of great violence; they are covered with great fragments & dislocated by fissures. Yet I feel certain, from close examination, that there is no connection between this violence & the curvature of the strata. Many of the most arched pieces. were quite compact. & the equal curvature of the quadrant shaped block, I have already said, was destroyed & not caused by the cracks. Everywhere the quartz rock has been violently shaken, perhaps the curved strata show the most signs of it, from the partially filled & numerous veins, rendering the stone brittle.
I before stated, that on the northern sides of the hill, the strata dipped to N by E at angle of 50° & that the more central ones have their superior extremities arched. On this same
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line of crest, there are lying many fragments similar in structure to the quadrant shaped block, which I have so minutely described.
About fifty yards to the South & about twenty lower down on the Southern slope, again we meet with strata dipping at
the a similar angle, & to the same point, N by E. — In the narrow intermediate space, between the strata thus similarly situated, there are others, which are inclined at a small angle to the South & which form parts of the Southern slope of the crest. In (fig 5) Fig 5 the lines with dots are ideal but those without dots represent what I have actually seen. However strange such a figure appears, I think it cannot be doubted but that the original curvature. must have been somewhat similar to the line (L D H).
If the intire summit of the hills, to the depth of a hundred feet, was removed, as much has been, we should then probably only see a mass of strata dipping at an uniform angle to the North. Presently other instances of a similar structure will be adduced.
# The range, in which the last described hills occur, is three or four miles long; it has
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been observed, that in each hill a slight quaqua versal dip is perceptible, but that commonly the strata are inclined either towards the South or North. The three principal dooms, if they may be so called, are situated at different elevations. hence we must suppose the summit of the line of elevation has been undulatary, I use this expression to explain my meaning & not the cause of the structure.
In (fig: 6) Fig: 6 (A) represents the 960 ft hill, (B) the broad flat topped one & (C) the 700 ft hill, of which (fig: 3) is the supposed section. In this same ridge, there probably are many other curves, which I did not see in my partial examination. —
Proceedings southward, we cross a valley or low irregular country, where slates & sandstones are found, we then come (but a little to the Westward of the proper line of section) to the central & principal chain of hills. (a) omitted (a)
This range attains an elevation of about 1400 feet, but the
highest hills in the Island is M. Simon, upwards of 1500 ft, which stands
by itself, a little way to the North. The ridge extends in a W by S &
E by N direction, but
useless] added pencil in margin.
(a) The range attains a mean elevation of about 1500 ft; in the central parts of the Isld the highest points vary between 14 & 1700 ft. The ridge appeared to me to run W by S & E by N. but the line of greatest elevations, as laid down in the chart extends in a W & E direction; towards — — (see following page)
towards the western extremity. it bends up more northerly. The usual quartz rock is here universally present & in in it. the black atoms, like mica, frequently occur. On the northern slope there is a nearly general dip, at a common inclination, to the North. The summit is irregular & every two or three (?) miles broad; in its central & southern parts the strata commonly are horizontal; great masses of these being much fractured & torn, often show resemblances to walls & ancient buildings. On the extreme southern edge of the range, the strata are vertical; the extremities of some of them are arched in such a manner, as to give rise to the idea, that they have once been united in a continuous curve, to the horizontal beds. which are only a few yards distant. (see fig: 7) Fig: 7
In some distance, along the edge of the hills, some such curvature appeared formerly to have extended. Some of the curvilinear fragments, which I measured, although two & three feet thick & only four or five long yet had been arched to a very remarkable degree. How pliant, so short & thick
useless] added pencil in margin.
a layer must have been, to have undergone such a flexure, & at present to exist solid & unbroken!.
These vertical strata on the southern slope, the horizontal ones on the summit & those with a northerly inclination on the opposite side, together make a kind of anticlinal line. But as the width of the range is so great in proportion to the height, the mass of hills perhaps are composed of many similar curvature, which imagined structure is represented in (Fig: 9) by dotted lines. The southern slope of the range is steep, we meet near its base, as near its summit, vertical strata; in one part within these vertical beds, there was a small, but very regular archway, with upright sides. I have shewn. that the line of elevation of one range was undulating, & here it appears in a transverse section of another, that curvation in a like manner occur at very unequal heights. The configuration of the quartz strata, may be aptly compared to an enormous swell, caused by any great & remote disturbance in a fluid. There
1 Presumably a reference to Bartholemew James Sulivan (1810-1890), second Lieutenant on the Beagle.
Sulivan tiles] pencil in margin.
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would arise, in such a case, parallel lines of waves; & in each line, there would be points of unequal height. & in each such point or wave smaller undulations.
To the southward of the main chain the country when viewed from a height, appears level, its is however furrowed by many small valleys & ridges, which generally run parallel to the greater ranges: These furrows are however intersected by many irregular winding arms of the sea. The rocks are either coarse blue clay. slates. sandstones. or those intermediate kinds passing into pure quartz rock. From a small Isd (Eagle Isd) on the south coast, a specimen of coarse compact blue clay-slate was brought to me. — The structure of these formations is so obscure, that it is scarcely possible to distinguish planes of fissure, cleavage, & stratification: an E & W direction was however certainly prevalent.
In this low country the irregular NNE
section, which I have partially described, ends.
But I have a few facts to mention respecting the central range, in a part 15 or 20 miles
distant. to the westward. The line of hills
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near the western extremity of the island, sinks in elevation & are, rather suddenly, deflected from their W & E course, to a W. 35° N direction. It was not a little remarkable that in the low country at the fort, the slate likewise was directed. W 30°-40° N. the inclination being vertical, or at a very high angle
to the northerly. At the only spot, where I examined the range, I found the quartz strata dipping to S 55° W, which is a greater change, than happens in the direction of the hills, or of the laminae of slate; but from the common tendency to a quaqua versal dip the position of the quartz strata can hardly be ascertained from single observation.
At this part of the mountain side, there were two rugged little hillocks situated twenty yards apart from each other. Fig: 8
In both the strata of quartz dipped very regularly at an angle of 40°, to S 55° W. S On the basset edges of the southern one, the extremities of some of the lower strata.
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were arched in a very trifling degree; of which I attempted at the time to copy with accuracy (fig: 8). — I can only understand these forms by supposing that the strata were formerly continued in the manner shewn by the dotted lines, & have since been removed. If from the hillock a few more fragments should be broken off, there would not then
some exist as in the case before described the slightest trace of any curvature. — Who would not, on beholdings hillocks so close together & with a similar stratification, have believed, they were parts of one mass of superincumbent strata?
Who would have imagined that an archway has been interposed in so short a space? —
In order to render my description of the section more intelligible, I have drawn a diagram (Fig: 9) Fig: 9. which will show the relation of the different parts. The lines drawn beneath the outlines represent the stratification & as before, the dotted ones are imaginary.
The lines crosses the eastern end of the island, at an average NE & SW bearing, but the section is supposed to be at right angles to each individual hill or range. the only
N B. There is also a miserable ground-plan to illustrate the same parts
N B. ... parts] pencil in margin.
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part, respecting which, no general remarks have been made, is to the north of Berkeleys Sound.
Here the strata in the various low ridges are all inclined towards one side. Perhaps in many cases, as has been shewn in detail in two instances, there originally was an archway (marked in a central ridge by dotted lines) with parallel sides. This general structure, under any hypothesis, is not of easy explication.
Having now finished
my the description of the formations of the Eastern Isld for the sake of connection, I will at once, explain, as it appears to me, their hypothetical origin.
We see the quartz rock has a granulo-crystalline, & sometimes even an arenaceous structure, & that it graduates into slates & sandstones. We also have indisputable proofs, that the whole thickness of the quartz has at one time been in a semi-fluid state. If we suppose, a mass of stratified sandstone,
to be covered by a gradually to pass gradually into overlying clay-slates, mingled with other sandstones, and the inferior parts to be subjected to so intense
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an heat, as to become partially fluid, we then can understand the gradation of character from crystalline to sedimentary rocks. Moreover if the faces from below should act upwards in certain lines & points of elevation, the lower parts of the semi-liquefied sandstone might be propelled through the superior strata, & assume, upon cooling, curvilinear forms.
If Subsequent degradation (which I believe, in this land has taken place to a great extent) would remove most cases of direct superposition, & the rock of intermediate character would border the sides, of the hard quartz ranges. now standing out more prominent.
All this is in accordance to what has here been observed. Indeed the simple fact of a preexisted state of semifluidity nearly proves that heat must have been the agent, for if not so, the rock
had must have remained unconsolidated, (& even in that case it might be doubted, if the consistence could be pasty & adhaesive), whilst the whole
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formation of quartz & of the superincumbent beds containing seams of fossil shells, were accumulating. — which is highly improbable. —
Arguing then on the Plutonian theory, as the strata, now in view, have formerly been rendered semi-fluid by the action of heat proceeding from the more central parts of the globe, so we must believe, that at some depth beneath the surface, the matter was more perfectly liquid: And, when we see the present hard strata imitating the undulations, of a great swell, we are driven to suspect "that the propelling power had actually moved in the form of certain great waves". Moreover, as in many of the hills (the height of some being little short of 1000 ft), the strata all belong to one system of curvature, the propelling wave must have been of nearly similar dimensions. I do not at all state this fact as proved, but it is a strong
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presumptive argument in favor of a paroxysmal movement; in mountains, where the strata, during the act of elevation, have been fractured this inference cannot with any certainty be drawn. A sold arch alone bespeaks unity of time, in its construction. With respect to the smaller curvatures, especially where they occur on the flanks of higher hills, probably they have in the greater number of instances, been caused by a lateral pressure, doubling the pliant strata, as when the two ends of a book, or bundle of paper, are pressed together with great force. The strata where not decidedly arched are always smooth & not undulating, with this difference, these curvatures, on a gigantic scale, may be compared (and probably also in their origin) to the configuration which is so commonly observed in the quartzose layers of mica slate. There is yet one fact, in the hypothetical origin of this island, which remains quite unexplained. It
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is the coincidence in direction between the laminae of slate
& the strata of quartz, which latter alone owe their present position
not to original formation, but to lines of subterranean disturbance. Over
the whole eastern extremity of this Island, the slate almost without exception
is directed (with small variations) in a W by N & E by S line; in a similar
manner all the principal ranges of hills & the quartzose strata, of which
they are constructed follow
about average W & E direction. Where
the hills have changed their course, the slate at their foot follows the new
line: when those quartz rocks, imperfect in character, at last pass into a
laminated sandstones or a clay-slates; have they not been seen to assume the
systematic cleavage? It is impossible to deny, that there exists between these
phenomena some close alliance: but what that connection is, it is difficult
It would however certainly appear that the
cleavage] added pencil in margin.
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lines of upheaval, have followed those of cleavage, because the latter must have been determined, shortly after the period of deposition of each stratum. —
The general surface of the land is covered by a thick
of bed of peaty soil or peat. In a part near the settlement, it attained a thickness of twelve feet; the lower parts of the peat were extremely heavy (1132) & compact & bore the signs of great age. The more fibrous kinds, not so deep below the surface are dug for fuel. The peat very commonly rest on a white clay, the origin of which latter substance is rather ambiguous. I was also at first much surprised at the quantity of peat; those species of plants, which in Tierra del Fuego are most efficient, do not here abound, nor, as in Europe, are the pools filled with living mosses. From the manner in which bones of cattle, shewed on the surface of the ground, are becoming enveloped, it appears that the coarse grasses themselves, & a few other
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plants, are the sole agents. I should think, no where could there be found a climate so favourable to the production of peat; even on the edges of masses of angular fragments this substance is rapidly extending its spongy
table covering. The sides & bottoms of all the small streams are scarcely passable on horseback from the same cause. —
The protection from wear & tear, thus afforded to the underlying rocks, must be more complete than perhaps in any other situation. With respect to the figure of the land, no map exists which pretends to follow every winding of the many creeks. These arms of the sea intersect the low slate country to the base of the central backbone of quartz: their channels are narrow & not deep; mud in large quantities has silted up. the upper extremities & even converted them into dry land. They are bordered by low cliffs of stone. So still & motionless is the water, that, the impurities not being removed it scarcely supports a living creature. Under such circumstances the channels cannot have been excavated. If we
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take the analogy, drawn from the mainland of America — & believe in a prolonged elevation, of which fact in recent times I could however perceive no evidence, the sea at a different level must have possessed more efficient powers.
Before the last elevations, likewise, the white clay, which underlies the peat, might have been deposited. — In connection with the present superficial state of the land, there exists a class of facts of a most remarkable nature. Several voyagers have mentioned the "streams of stones" & Pernetty, the early historian of the Falklands, has devoted a whole chapter, & an engraving, to their description. In many parts of the island the valleys & hill sides are covered with an astounding number of great angular fragments of quartz rock.
These vary in size from a man's chest to ten or twenty times as large; & occasionally such measures are altogether exceeded.
The blocks show not the slightest signs of being water worn, their general outline
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is angular, but with the edges &
corners points slightly
blunted; they do not occur thrown 20 together in to irregular piles,
but spread out into level sheets or great streams. The It the
is not possible to ascertain the thickness of these masses beds; but
the water of small streamlets could be heard, many feet below the surface
trickling through the stones; & that depth probably is too little, because
the crevices between the lower fragments being must have been long
ago filled up with sand, & the bed of the rivulet thus raised. —
The width of these sheets of fragments varies from a few hundred
feet to a mile:
clearly but the peaty soil daily encroaches on the
borders, &, whenever a few fragments lie close together, even forms so
islets in the midst of the stony waste. In a valley south of Berkeleys Sound,
which we called the "great valley of fragments" it was necessary
to cross an uninterrupted band half a mile wide, by jumping from one pointed
stone to another stone; being overtaken by a shower of rain we easily
found good shelter beneath one of these huge fragments. —
20] pencil insertion.
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¶ Far the most remarkable feature in the "streams
of stones" is their little inclination: on the hill sides
I have seen level extended masses dipping at an angle of ten degrees
to the horizon; but in some of the level broard-bottomed valleys, it is was
not more than sufficient to be clearly distinguished. On so rugged a surface
I had there was no means of measuring the angle; but to make
give a common illustration, I may say that the inclination slope would
not check the speed of an English mail coach. — An uninterrupted sheet
In some places a continuous stream of these fragments will sometimes
follows up the whole course of a valley & even extends to the very crest
of the hills; there, huge masses, exceeding in dimensions any small building,
seem to stand arrested in their headlong course; there also the curved strata
of the archways lie piled on the ground over each other, like ruins
of some cast & ancient cathedral. But I feel quite at a loss, when
I attempt to decide In endeavouring to describe these scenes of violence
& desolation which pass in my mind one is tempted to pass from
one simile to another without satisfaction: perhaps the most faithful
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one idea one, is to imagine or streams of white lava to have flowed from many parts of the hills mountains into the lower country, & these when consolidated, to have been sent by some enormous convulsion into myriads of fragments. The expression "streams of stones" which immediately occurred to every one, conveys the same idea, as the simile of the lava. These scenes are perhaps rendered on the spot more striking, by the contrast of the low, round forms of the neighbouring hills. I was much interested by finding on the extreme summit of a hill about 700 ft high ( part of the same range, in which the quadrant shaped block was situated) a great arched fragment lying on its convex or upper surface. — Must we believe, that it was fairly pitched up in the air & so was thus turned?
Or with more probability, that
anoth formerly another part of the same range stood above the point, where this monument of a great convulsion of nature, now lies.
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The presence of the streams of blocks. is not confined to the eastern island; Mr Kent described to me with accuracy similar cases, which he had observed, at West point; (the extreme western point of the whole group); at Swan isld; & at Port Egmont.
When we come to reflect, concerning these phenomena; we must first observe, that the convulsion, which has dislocated the strata & poured over the low country, the fragments torn from the sides & crests of the hills, has happened subsequently to that earlier one, when the semi-fluid stone was modeled & elevated into its present form. As the fragments are not rounded,
& nor the crevices are not filled up with sand, or other matter, we are induced to believe, that the period of violence occurred, after the land had been raised above the waters of the sea. Giving reins to the imagination it is difficult to comprehend any force,
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powerful enough to roll angular fragments of great size along
a surface both rough & little inclined. In a transverse section
cross a stream of stones lying across within a valley, the bottom is nearly
level or rises only a trifle but a very little towards either side:
hence the fragments appear to have traveled from the valley's head; but in
reality, it seems more probable that they have been hurled down from the nearest
slopes, & then by a vibratory movement, of an overwhelming power have
been leveled into one continuous sheet. * (a) note (a) If, during the earthquake,
which in 1835 overthrew Concepcion or in Chili, it was thought wonderful,
that small bodies were pitched a few inches from the ground, what must we
say to a movement which has caused fragments many times in weight (like so
much sand, on a vibratory board) to move outwards & find their level?
I have seen in the Cordilleras of the Andes, the evident marks where stupendous
mountains have been broken, into pieces & like like so much thin
crust & the strata thrown
Note] pencil in margin.
(a) Note. An inhabitant of Mendoza & hence well capable of judging, assured me that during the several years he had resided on these islands, he had never felt the slightest shock of an Earthquake. —
on their vertical edges, but never did any scene, like
of the "streams of stones", so forcibly convey to my mind, the
idea of a convulsion. of which in historical records, we might in vain seek
for any example counterpart. — (a) 20
In the beginning of this chapter, I stated that the geological structure of the Western Isd was extremely similar to that of the Eastern, which we have described. Mr Kent procured specimens from the following places. — C. Meredith, 1890 the SW extremity of the island is composed of a quartz rock. containing in its interstices. white aluminous powder. — At West Point, the NW extremity, the quartz varies in its nature, being more or less hard & granular, sometimes ferruginous or containing the aluminous powder & not unfrequently black specks of imperfect mica. —
Intermediate between these places & more to the westward, Drew Isld is situated; a series of specimens 1886 ... 88 from that place show a gradation in character from a granular quartz rock to a very impure variety 1889 in which a coarse mechanical structure was very evident.
20] pencil insertion.
(a)] deleted in pencil.
W. Island] added pencil in margin.
(a) Mem: ask. Prof. Sedgwick1
In N. Wales. near Barmouth I remember being struck with a great sheet of angular fragments inclined at a small angle: it was near the borders of a lake, not far from a country house of Sir. T. Mostyn. —2
1 Adam Sedgwick (1785-1873), Woodwardian Professor of geology, Cambridge University, 1818-1873.
2 Corsygedol north of Barmouth (‘fly-fishing in the Corsygedol lakes’ was one of the ways Darwin passed his time at Barmouth in the summer of 1828: CUL-DAR112.B.58). [note by Peter Lucas]
All the Islets on the southern shore, are composed of the same varying quartz or siliceous sandstones. On the northern shore; at White Rock harbor, the quartz is pure, white & compact, yet a granular form was distinguishable. At S. Carlos bay quartz with the aluminous powder.
At Port Egmont, the most abundant variety is a hard compact dark brown micaceous sandstone 2058, it seems to belong to the kinds which I have called intermediate. From Mr Kent's remarks & these specimens, it appears that the quartz formation, bears a larger proportion to the softer rocks than in the Eastern isld.
On inspection of the chart, made on board the Adventure, the whole western
extremity coast will be seen to terminate in points & the sea to be strewed with linear shaped islands, in both of these a direction of nearly W 25° N, is found to be very prevalent; this line does not differ widely from that of the Eastern Isd. — The granular quartzose rock, which contains the soft aluminous substance & the black specks of mica, appear rather a curious variety of a mountain rock.
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I was therefore interested by finding so perfect an identity in nature of these strata, on the extreme opposite sides (distant 130 miles) of the archipelago. I should apprehend there are few instances of a quartz formation, on a more extended scale: already in S. America, two large ones have been described, one in Brazil & the other in Peru.
V Humb: Superpos:1
Synopsis. Looking to the neighbouring coast, to which the Falklands
are attached by a bank of soundings, we see in Tierra del Fuego a grand system
of clay-slate: how
far closely the formations of the two countries
are geologically related I have no means of judging; but certainly in both
cases the fissile structure of the schists & the outline of the land follow
one & the same direction. On the shores of central patagonia quartz rock
was found; & in northern Patagonia the ranges of the S. Ventana are entirely
so composed, whilst those of Guitru-guigù, a little distance to the
northward, consist only of clay-slates: over the whole of that country the
rocks are divided in a W 35° N. line. —
1 A reference to Humboldt 1819-1829.
V Humb: Superpos:] added pencil in margin.
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I had requested Mr Kent to collect a box of pebbles from any beach on the northern shore; those which he had the kindness to bring me were picked up at hazard in White Rock harbor, at the entrance of Falkland Sound. (a) The pebbles were well rounded * & varied in size from a walnut to an hen's egg, & some few larger.
X enter in proper chapter
Out of the whole number I recognized 38, as certainly belonging to the neighbouring formations; 26 as intirely similar to the shingle which covers in so immense a sheet, the plain of Patagonia; & lastly about an equal number of the relation of which I did not feel sure. The pebbles which resemble those of Patagonia are Porphyries; of such, a pale colored feldspathic kind, with crystals of white feldspar, is most abundant, as likewise happens at S. Cruz. one of the nearest parts of the mainland. Amongst the rest I instantly perceived one pebble of a kind which is especially common on the plains near Port St Julian; it is yellow siliceous porphyry possessing a very peculiar & well defined character. —
X enter in proper chapter] pencil in margin.
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But can we believe that these pebbles have traveled over a space of 350 miles, from the Patagonian shore? In support of this view I must state, that a line of soundings carried across the intervening sea, no where showed a greater depth than ninety fathoms; the bottom was smooth & regular; with the sand there came up minute pebbles of a tenth of an inch, or less, diameter, composed of yellow, dull red, & black, rocks which were all fusible under the blowpipe; the proportion of siliceous sand decreased as the Falkland isles were left astern. (a) (a) omitted
But there is another view of the subject; about 15 miles distant from White Rock harbor, on the shores of a large island, called Pebble island, great numbers of small agate pebbles are commonly found. 3598 (b)
From their form & opake coating, I suppose they owe their origin to some neighbouring amygdaloid rock. Now if such formations occur here, likewise porphyry rocks may lie concealed beneath the sea; & we have
(a) Moreover in many parts of the neighbouring seas, even as far as near Staten land & on the east coast of Tierra del Fuego, pebbles were brought up by the lead, which I could only attribute to the same bed of shingle. On such a supposition, the distance of the parent rock is indeed great*; for we must look to the mountains of the Andes as the source of the chief part of the pebbles which lie scattered on the Patagonian coast.
(b) The pebbles are likewise found on White Rock harbor itself. — so the sentence must be altered — specimens came from there. —
*. About equal to the space from the Pyrenees to the London basin. —
(b) The pebbles...came from there. —] added pencil.
seen in central Patagonia; that an extensive porphyry formation is, there, associated with one of quartz. I am quite unable to determine, which is the most probable of these two methods of accounting for the unexpected presence of such pebbles on the shores of this archipelago. —
Having finished the description of these islands, it will be
highly well briefly to recapitulate the more important observations.
(1st) The satisfactory manner in which the theory of metamorphic action by heat, accounts, for, the gradation in character from the quartz, through the intermediate rocks, into the slates & sandstones; for the softened & pasty condition of the strata; & even perhaps for the appearance of imperfect crystals resembling mica. It is not difficult to believe, that if this action had been continued with increased intensity, granitic rocks would have been produced. In attempting to imagine the state of the rocks of these islands
214 verso [blank]
before the period of metamorphic action; a very close resemblance will be found with the grand sandstone formation of New S. wales.
At that place, sandstone strata, to a great thickness, are composed of grains of quartz loosely cemented by a white pulverulent matter, and they are usually covered by other beds alternating with clay-shales: there is however this remarkable difference, that at the Falkland's the slates cleave, with a high inclination, in a certain fixed direction, whilst in Australia the laminae of shale are either horizontal or have no determinate position. —
(2.ndly) That the same principle which gave to the rock their system of uniform cleavage, likewise possessed the power of separating the constituent parts of clay-slates & sandstones; that its action appears to have been opposed by ordinary gravity: — hence where the sandstone was abundant, or was coarse & contained organic remains,
N B. Mr Lesson Zoologie of Coquille's Voyage.1 considers my quartz a very quartzose sandstone: general description of the rocks agree, but not their superposition: account of the "streams of stones" partially agrees; but does not reason from it: alludes to a hill of ruins of Pernetty:
A passage about the cleavage, not clear to me; & totally different to my statements:
Describes Peat: no mention of structure or origin of the whole island: —
page in pencil.
irregularly horizontal strata were formed, in place of
the inclined laminae. Do we not here see a reason, why in the perfectly fissile slates, extraneous bodies are seldom found? for if present, that structure would have been destroyed; & lastly that, after successive periods, shewn by intervening strata, a cleavage, similar in every respect, continued to be impressed on the slaty rocks. —
(3rdly) The parallelism of the line of cleavage with those of elevation & consequently with the outlines of the land & the longer axis of the whole group. —
(4th) The peculiar forms of the arched strata of quartz; & the considerations which indicated a sudden & wave like movement of the inferior liquefied matter, as the cause of the greater curvatures in the sold crust.
(Lastly) The scenes of violence, so plainly recorded by the wide monument of the "streams of stones". — I may add, it is a singular & perhaps more than an accidental coincidence
(Turn over) (a)
(a) that at different periods, the subterranean forces should twice have displayed on the same theatre, their most overwhelming powers. —
N B. Capitel letters are placed improperly to many of the rocks & names of points of the compass (&c)
N B. ...compass (&c)] added pencil.
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Citation: John van Wyhe, editor. 2002-. The Complete Work of Charles Darwin Online. (http://darwin-online.org.uk/)
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