RECORD: Darwin, C. R. Geological diary: Tierra del Fuego. (1-2.1833) CUL-DAR32.98-122 Transcribed by Kees Rookmaaker, edited by John van Wyhe. (Darwin Online, http://darwin-online.org.uk/).

REVISION HISTORY: Transcribed from microfilm by Kees Rookmaaker, corrected against the manuscript and edited by John van Wyhe 7.2010. RN2

NOTE: This document, part of the largest scientific document composed by Darwin during the voyage of the Beagle, is written mostly in ink, except where noted. 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.


98A

[hand coloured sketch]

Ponsonby Sound
Fig: 2

2 or 300 yards wide

North & South section: slate dipping to the SW, With various lines of subsequent elevation

98A verso [not microfilmed]

P. 81

P. 81] added pencil.

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Navarin Isd

have altered its direction. — At about 5 miles East of the entrance into Ponsonby Sound there is a large amphibolic formation. — The slate near it dips to SSW ∠ 75°: at the junction the greenstone (specimen 940) 940 hornblende & greenstone alternates with the slate. The direction of the bed is a little disturbed, but the sides are parallel. at the point of contact the slate is very fissile, at the same time harsh. — much harder & more sonorous, of a reddish colour, with minute scales of mica. 941 — Within the main formation, the rock is chiefly composed of large crystals of hornblende 938 (some nearly 3 inches long) feldspar & a green mineral? — It varies however much in its characters. 939 — This formation appears to extend for a mile or two in each way: —

At the East entrance of Ponsonby Sound, the slate is crossed by many dykes of greenstone (943). 942 943 — The cleavage here actually dips ENE. — The slate in contact with the greenstone is altered into a compact blueish-grey, heavy rock; having an angular cleavage 944: it contains minute specks of Pyrites; it fuses easily into a pale glass: it would appear to be a compact feldspathic rock. —

On the opposite side of the Entrance there is an abundance of different varieties of Greenstone [porphery] 965 one variety, crossed by small dykes, occurring in the midst of slate, with a southerly dip. —

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Navarin Isd

To the South of the line which joins the two last mentioned Greenstone formations, & within the Entrance, a perpendicular & lofty cliff of slate presents a curious scene of disturbance. — The section is nearly N & S (a), so that the SSW dip is generally visible, but with this the beds are in several places curved into domes, & in one or what is more probable into arches. —

cleavage or strata curved

& in one place, the up-heaving force. has been sufficient to burst the roof & has left the sides nearly vertical. This last contortion is on a great scale, as the broken walls at the summit, are 2 or 300 yards apart. — Fig: 2. rudely represents this appearance: — This disturbance of the slate is perhaps of the same date, as the protrusion of the described amphibolic formations. —

On East side in centre of Ponsonby Sound the slate is intersected by several broard & vertical dykes of greenstone Trap. — This latter is in such a state of decomposition as to resemble clay, containing crystalline nodules. The narrow beds of slate are here bent & contorted in every direction; near to one large dyke. the strata are suddenly twisted from below into quite a contrary direction from the prevailing one: —

On the West side of Ponsonby Sound Capt. Fitz Roy noticed some Trappean rocks cutting through slate. These in their mineralogical characters

cleavage or strata curved] added pencil in margin.

99 verso

(a) 1834 Feb: These appearances are on the Navarin side, on the opposite shore, I observed one arch in the slate, which shows that the line of disturbance crossed Ponsonby Sound, & since that time this channel has been cut through.

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are singular — it would appear to be an imperfectly crystallized Greenstone. 997. ... 1000 & from containing hard nodules of a more crystalline natures it weathers very unequally & hence assumes a most singular resemblance to a Breccia or Conglomerate. —

apparently ancient volcanic vascular greenstone

The interstices containing Carb of Lime adds to the deception. — Capt. Fitz Roy mentions that the rock externally was very irregular & resembled those of volcanic origin. —

The whole SW extremity of Navarin Island is composed of trappean rocks Green [illeg], but I had little opportunity of examining them 965. In extent & appearance these latter imperfect greenstone would seem to be allied to the great formation of the SW coast. — Indeed my only reason for separating the Amphibolic rock in Navarin island from those of the SW coast, is the local distance. — We may imagine that the former burst through the slate, immediately subsequent to the elevation of its ridges; but that it owed its origin to the same cause. which produced the Trappean rocks in the SW coast. — (a)

To conclude with the slate. — The slate, as has been said, extends along the northern shore of the Beagle Channel to within 5 miles East of the bifurcation; here it seems to rest conformably on the Gneiss & Micaceous schists:

apparently ancient volcanic vascular greenstone] added pencil in margin.

Green [illeg]] pencil insertion.

Indeed my only reason...SW coast. — (a)] cancelled.

100 verso

(a) 1834 .. Feb I ought to have stated, that I examined in many places the East coast of Navarin Isd & found no difference in character of the slate, & the general SSW dip. — During this visit, the NE point compact blue slate dipped ∠48° to the South: WSW of Picton Island, the slate in Beagle channel the slate, was contained planes of harder greyer varieties (which I have called jaspery). — in two sites they dipped within one degree to the SSW, or at an ∠ 72° — the other 59°. — The rounded summit of the nearest hills which is 2000 feet high was composed (Mr Bynoe brought specimen) of a blueish rock 1873 with numerous small crystals of feldspar. I may here notice, that some of the ranges of hills south of the Beagle Ch. in colour, form. manner of degradation & dip of superior beds &c. very strikingly resembled M: Tarn. —

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To the South of the Channel it extends to the West of the bifurcation & runs up on the West side of the Northern arm. — This arm being a valley between the older & these slates. — I imagine the slate extends across Hoste island in a SSE line, till in Hardy Peninsula it becomes blended with the Trappean rocks. — On the W side of the peninsula of (more modern) slate, where it crosses the southern arm, micaceous schists & granitic rocks occur, so that this slate is both surrounded by & rests on the old crystalline formations. The slate at its extremity alternates with & intersected by 2 varieties of Trap 953, the one abounding with Hornblende the other with Feldspar. — The cleavage is here disturbed from its proper direction. —

Cleavage & strata

I observed, in the Beagle Channel, the same white, waving bands & seams which I ment described as horizontal in Navarin Island, here on the sides of the mountains, they dipped at a small angle to the SSW, but were very distinct from the cleavage. — changed strata In the north arm, facing in an escarpement facing the micaceous schists, these bands were most distinctly visible dipping to the SSW; they here especially seemed to mark the planes of stratification. — it certainly at is a strong argument these being found horizontal in the low country of Navarin Isd, but inclined when occurring on the sides of the mountains. At the base of these mountains I remarked in several places, but with no great accuracy

Cleavage & strata] added pencil in margin.

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that the cleavage dipped in a contrary direction (viz. NNE) to the prevailing one towards the hills. — I only mention this, from Von Buch,1 having seen this fact in Norway. —

Granite formation I will now describe the Crystalline rocks on which the above-described slate lies. — This formation extends from the point West of the bifurcation in the Beagle Channel, to the outer islands, a distance about 60 miles. To the South it extends across the southern arm & perhaps about half way down Hoste island. In the North, of it probably includes M. Sarmiento & is said to extend through South Desolation. — Where we first meet in the Channel. it varies much in character from good mica slate to Gneiss & Phyllade (or where the constituent parts are not discernable): Specimens 949. 950. 951 949-951, are some varieties: The cleavage here dipped to SSE instead of the usual SSW. perhaps in consequence of this being the termination of the ridge. —

cleavage

The planes of cleavage were here tortuous & involuted. in a similar manner as the knots of wood; layers of quartz of some thickness following the bends. — I noticed. that this tortuous cle arrangement of the constituent parts was very general (a), while in the clay-slate the planes of cleavage were as remarkably straight & regular. — Proceeding up the northern arm, we pass mica slate. Hyalomictite. Phyllade dipping to the SSW, & soon afterwards come to a grand. mica slate formation

1 Buch 1813.

cleavage] added pencil in margin.

102 verso

(a) March The tortuous & waving lines of cleavage has been the subject of much discussion. — Ramond (in Greenough P 79)1 eloquently attempts an explanation by the meeting of currents. — In this case the planes, although folding one with another, have a well marked general direction the same as the smooth laminae of the slate. — Hence the cause in both must be the same in principle, although varied in kind. — It is evident currents of water must be have been entering about in order that the great regularity of the clay slate may might be produced. — We cannot therefore think they were present during the formation of the crystalline mica slate. —

1 Greenough 1819, pp. 79-83.

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Granitic forms:
This rock is composed of curved layers of quartz separated by scales of mica & containing numerous dodecahedron Garnets. 952 (a) — This serpentine cleavage dips to SW by S, or SSW, at ∠65°. — Here the mountains are very lofty & steep, their summits are covered with perpetual snow, from which glaciers extend to the waters edge. — Their height perhaps is between 4 & 5000 feet. — This mica slate dips directly towards the northern arm & the Escarpement on the opposite side is the clay-slate. — At the base of these lofty mountains are numberless angular blocks of Granite. so that I have no doubt it forms the central part of the chain. —

Proceeding onwards we meet varieties of micaceous schists (954) 954, 955 & Hornblendic mountain slate. dipping to the usual point. — There are seen resting on large rounded & most desolate hills of granite. — 956 Granite with large crystals of quartz & little mica. — This is met with to the N by E of Cooks Bay. — From this point to the Wes East end of Stuarts island. Mica slate. Gneiss. Phyllade & Granite are met with. — north of Gordon island there is a granite in which the mica is partly replaced by a green mineral 957 chlorite & the constituent parts are on a large scale so arranged as to show a tendency to become Gneiss. —

Again we have (in a large North newly discovered island) Hornblende slate 958. 959 & an imperfect Gneiss dipping to the SSW. — Near to this is a

'chlorite' '958. 959'] added pencil.

103 verso

(a) It has been said (Greenough P 62)1 that Garnets are only found mica slate, where the cleavage is, as in this case, in waving lines: At Rio de Janeiro there is an exception to this rule. —

strata & dip of cleavage identical

1 Greenough 1819, p. 62: "it is said that garnets are never found in this description of rock, [mica slate] unless where it is waved."

strata & dip of cleavage identical] added pencil.

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Granitic forms:
large extent of massive, barren hills of Granite. — These granite hills were not lofty. — At the most westerly point there was much Syenite. —

960 [active] hornblende [active]mica

The only other place where I visited this formation was in southern arm of Beagle Channel, where rounded hills, on both sides were formed of a rock. which I suppose to be syenite: the quartz no was in small quantity 962, 963 (b) mica & Hornblende abundant. At the point where this rock is covered by the clay slate, micaceous schists occur in it. —

The only place where I examined the western island. was the East end of Stuarts Island, which is Greenstone & the East of Londonderry which is Hornblende slate. 961 — From what I hear, it seems the greater number of the western islands are greenstone (a); now whether this belongs to the granitic formation, or to the Trappean one, which will be presently described as forming the West side of Hardy Peninsula, I have no means of ascertaining. — Perhaps an examination of the specimens brought home by Capt. Fitz Roy during the last voyage may help to explain it. —

Hardy Penin:
The geology of Hardy Peninsula is interesting. The Beagle was anchored in a bay north of Orange bay; in crossing from this point in a West direction we meet the following rocks. — On the coast, there is good

104 verso

(a) The external forms of the mountains in these islands, were perhaps most like that of Granite —

(b) Whatever this rock may be in mineralogical character it is clear it belongs to the granitic formation. from in its upper part alternating with Micaceous Schists : —

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Hardy Penin:
clay-slate (such as we have seen so general) but in no great quantity. — The most rock is a blueish-grey compact feldspathic rock one; somewhat resembling specimen of altered slate (944). — This rock is more generally has an angular cleavage 975 sometimes even showing tendency to be columnar: 996 in many places it was distinctly slaty & I recognized a dip to SW by S. — From these rem facts & the resemblance to (944) I imagine this rock to be altered clay-slate. The hills here are not high: & of an irregular form — at some miles distance to the north, the regular slate range may be seen. — Near to the west coast there is a very remarkable hill: it is of a saddle-back shape & the most lofty in the neighbourhood. — the lower part was formed of a fine grained Hornblende rock in which there are yellowish spaces 1015. 1016. free of the Hornblende crystals; fracture conchoidal. — The flattish summit of the mountain is formed of several rocks. — the principal one is a slaty sandstone, which clearly rests on the hornblende rock: it dips towards the sea, or to the SW by S ∠ 25°. — & the basset edge fronts the East. —

The slaty sandstone, scarcely deserves its name 1017, 1018 (([Teagomite])), it is of a blackish grey colour, & semi crystalline — it contains in dusty cavities numerous small white crystals & form an intimate mixture with some mineral

[Gesmondine]

'(([Teagomite]))' & '[Gesmondine]'] added pencil.

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Hardy Penin:
it is fusible. — This rock in several places formed irregular quadrangular columns. Together with the above there was a sonorous. brittle, semi-pellucid, fisible, feldspathic rock 1019, with an angular or prismatic cleavage. (a) — Also a red porphyry, where the base is earthy 1020 & merely with white specks. — All these rocks were regularly superimposed on the Hornblende rock. —

I could not help conjecturing that as the cleavage or stratification show. they were originally ? beds, in the clay-slate formation & now altered, & that even perhaps the Hornblende rock in the slate melted. —

As I have mentioned to the north there is a regular slate range. but in the South. the view extends over numerous, rough, barren & irregular paps: — These I examined several of them; they are as various in their mineralogical nature, as in their external form. — Out of 5 or 6 neighbouring hills, one was Hornblende, with fine crystals: — another a Feldspathic rock with crystals of Feldspar 990 & acicular ones of Hornblende: another good greenstone 988, sonorous, prismatic cleavage, together with a Hornblende rock, in large crystals, & containing great quantities of pyrites in veins. 989 — This rock decomposes into a bright red colour: — another was greenstone & feldspathic rock: the highest hill & surrounded on all sides by

I could not help...slate melted. —] cancelled.

106 verso

(a) The action of the weather had broken these rocks into small angular fragments. We observed on the sides of the hills that they were as closely packed together, as if deposited in water: This was explained by seeing that the melting snow softens the ground, to the consistence of mud; so that the stones arrange themselves in the from their weight in the regular manner:

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Hardy Pen
these crystalline rocks. was a slaty Feldspathic rock, resembling (996 & 975) the cleavage ran NW by W & SE by E, — This is very remarkable as showing the connection if not identity with the clay-slate formation. — Another extensive hill was of a very singular nature; the stone is basaltic (?) easily fusible & containing numerous yellow crystals 991, 992 993. It is divided into small angular concretionary pieces of the size of a nut; this gives the rock a most curious appearance; it is best seen in decomposing pieces. — On the large scale it is columnar, but not very regular. — The stone is of a uniform nature in the whole hill. — I have reason to believe a similar sort is found in the Gulf of Peñas. —

In the midst of the above described hills there is a mass of rock. resembling that found in external form at southern arm of the Beagle Channel 994. 995 & which I suppose to be a syenite. — If there is any foundation for my conjecture, that these trappean laminated rocks owe their origin to melted or altered clay-slate. — may not this syenite, this highly crystallized, massive rock. be the agent? (B)

That here from some cause, perhaps more immediate contact, the slate was fused whilst as in the Beagle channel, it rested on micaceous schists & was elevated into mountain ridges. — If this reasoning

That here from...reasoning] cancelled.

107 verso

(a) At first sight the concretionary rock bore a great resemblance to those of volcanic origin. —

I ought to have noticed the following fact. — This hill is quite distinct from any others & entirely composed of this striking looking rock, yet on the summit were many fragments of several varieties of greenstone, such as occur in the neighbouring hills. — The only way I can account for their presence is by some change in the elevation of the land subsequent previously to the present order of things. — or more probably action of water.

(B) I should suppose these Barathic & Porphyritic rocks have certainly been ancient points of subaqueous emption. —

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Hardy Penin:
is not thought too improbable; it may explain the whole SSW chain of islands (which are these irregular pap-form hills submerged which runs parallel to the gr main granitic moun line of mountains. —

Wollaston Isd In an island north of Wollaston & drawn in the chart as its most northern extremity, there is a curios Trappean formation. — The rock is of most various natures 1029 ... 1032; in some places contains many nodules & veins of agates. these when large are drusy 1033 & 1034 & lined internally by hexagonal crystals of quartz. — It is generally much decomposed & where most so is reduced into a sort of clay; this however containing rounded balls of harder & more enduring rock: from this cause the appearance is that of a volcanic formation. — Walking to the west, there are two alternatives of a Breccia on conglomerate with the above rock — the junctions were not very distinct. but I think the conglomerate dipped to the SE beneath the masses of Trap. — If the crystalline rocks had a volcanic appearance this had a still more striking one. — The fragments were either angular or slightly rounded; many of them of an immense size 1035, many several yards in circumference; they were cemented by an earthy base. — The conglomerate contained an endless variety of greenstone, some of them slaty: also a bright red hard scorice 1036 1037; a vesicular looking lava;

is not thought too...of mountains. — ] cancelled.

108 verso [blank]

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Wollaston Isd
also an amygdaloid with carb of Lime 1038: I should have suspected the neighbourhead of a volcano; V. Supra manifestly ancient volcano if the general features of the country did not disprove it; if I had not seen the varieties of rock in Hardy Peninsula & if the nearest hills, about 7 miles to the East had not been (as already mentioned ) a feldspathic rock with angular fragments of clay-slate. — As it is I only look on these rocks (b) as a curious instance of resemblance between volcanic & the older rocks. —

Mr Weddel in his "Voyage"1 mentions often finding (a) in this southern part porphyritic vesicular lava & supposes it owes its origin to Captain B. Halls volcano. — The place laid down by Captain Hall in Captain Kings chart is not above 8 miles from the Beagle Channel. — It is impossible that a volcano should exist in a regular slate range, & not show in its external form or character of vegetation its presence: or without leaving in the water courses pebbles, & I am certain not even pebbles of trappean rock like those of Wollaston Island are to be found in the Beagle Channel. — The appearance of flames seen by Capt. Hall is clearly to be attributed to the burning of forests. — in one place amongst others, the black stumps showed that there had been a fire of several miles in length. & of the breadth of the side of a mountain at no very long period since. —

1 Weddell 1825, p. 187.

I should have...older rocks. —] cancelled.

109 verso

(a) Weddels Voyage P 187: —

(b) As to the age of the Breccia I am quite ignorant

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Mr Weddel also states. that rocks given to the Edinburgh museum from Diego Ramirez & Il Defonsos. are said by Prof Jameson to Porph. Lava & Porph. Lava. — & Trap-Porphyry (P 169). — These rocks as well as the vesicular lava evidently belong to the same formation as the above described northern extremity of Wollaston island. —

Southern Isd
The most southern islands are evidently a continuation of the chain of the SW coast. — The rock is generally a simple greenstone, a mixture of feldspar & hornblende: the form of the mountains is extremely regular, being, a cone with curved sides; the peaks are isolated & hence gives to the outline a marked appearance. — Katers peak in Hermit island is the higest being 1700 feet. To speak hypothetically, we might here imagine the slate to have been more perfectly fused. —

Hermit I.
In Hermit island the rock is good greenstone with pyrites 916. 917 918; often with a slaty structure: it sometimes is almost composed of Hornblende: High up in Katers peak the rock contains is feldspathic, with semi-vitreous crystals of feldspar 919. 920 & acicular ones of Hornblende; it is highly sonorous, & abounding with parallel & smooth planes of cleavage; this is to such an extent, that the summit of the hill looks as if built with these angular pieces: — by the external form, & mineralogical characters. I was reminded of phonolite

To speak hypothetically...fused. —] cancelled.

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110A

[sketch map on tracing paper with water colour]

110A verso

[sketch map on tracing paper with water colour]

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Southern Isd
such as at Fernando Noronha & saw how easy the transition of the two rocks is. — I may mention finding numerous fragments, angular, of an impure, reddish, aluminous limestone in Wigwam Cove. 921 — I am quite at a loss to conjecture where they came from. 922 — Jordan Island is greenstone, Horn Island is likewise so. — & judging from appearance. all the neighbouring small islands & south part of Wollaston Island. —

cleavage
The more I reflect on the planes of stratification, cleavage & fissures seen in the rocks of Tierra del Fuego the more difficulties I find in the subject. — I will first define. what meaning I believe is attached to these terms. — Stratification includes an hypothetical idea of plebes, originally depos formed by deposition in an horizontal position. — Cleavage is the well known structure of slates. — Fissures are parallel divisions in the rocks, generally at wider intervals & which meet the planes of cleavage at various angles. The following contradictions have often arisen in my mind. — It is generally said, that the direction of cleavage & stratification is the same, but the inclination of their dips different. — I can understand (a), that from some unknown law, the original & slightly inclined (for if horizontal, no direction would exist) strata (b), might have the same range with the planes of cleavage: but suppose these beds, with cleavage & stratification dipping to the same point, but at different angles, to be tilted on one side; — suppose, a line

111 verso

(a) It is with difficulty I allow this; the original inclination of strata can only arise from the surface on which they have been deposited; & what connection can the direction of the supporting surface, have with the cleavage; which so many facts show to be intimately related to the chemical nature & crystalline structure of the rock. —

(b) By direction I means of course, the true bearing of the line formed by the intersection of the horizon with the plane of cleavage or stratification: The dip is at right angle to this.

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of elevation to cross these beds in any direction; then, excepting it should be the very one of original deposition, it must destroy all identity in a point of dip of the cleavage 7 stratification. — In this case, the (a) new direction of the strata will be nearly the same as the line of elevation, but that of cleavage different from both. — This must happen in the upheaval of the greater nearly all mountain chains. — Yet in Tierra del Fuego, there is a parallelism between the direction of cleavage & form of land: the great M. Sarmiento chain (in which is included much granite), runs in a WNW & ESE line (b); the general form of whole country leaving out the modern & subsequent formation on the East coast is parallel to this as are also many of the channels, such as west part of Magellan St, Gabriel channel, Admiralty Sound, North arm of Beagle Channel: the tendency, although this is more doubtful, on the east side to dip to the East of SSW, as in the West to the contrary direction corroborates the same fact: if we suppose the mountains & leasing vallies to be created by elevations, we must see a close connection, if not absolute identity, between the line of upheaval & direction of cleavage. In conn With respect to this subject, there is a geological fact in Tierra del F of difficult explanation: if we imagine the Sarmiento chain of crystalline rock to be the line of elevation, all the planes to the south, should, as we find them dip to the SSW; & those to the North of it

112 verso

(a) If the strata had been horizontal, the direction when upheaved, would be the same as the line of elevation; in the case supposed, the strata are originally slightly inclined, in order that they might possess direction & that this according to common statement, be might also be common to the planes of cleavage; hence when upheaved, the new direction is not identical with line of elevation. —

It is evident, in the case of horizontal strata, being upheaved, although the direction of strata & line of elevation will be the same, that of cleavage will be different, excepting in the rare case, where line of elevation. & original one of cleavage should be the same. — then indeed direction of strata & cleavage of line of elevation would all be the same. —

(b) I need not mention how general the WNW direction of cleavage is: — In particular respecting the main chain V P 70 (b): — (supra)

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to the NNE; in contradiction to this, in the East end of the Beagle channel, & therefore to the North of the probable line of upheaval we yet find the SSW dip. —

Every one acknowledges the difficulty of observing stratification in a slate district: In Navarin island. I have mentioned horizontal planes & waving bans of a white colour; here the country is comparatively level, but on the sides of the mountain these bands dipped at a small angle to the SSW. — This certainly looks like stratification. — In the former case however the planes of cleavage dipped nearly vertically to the same point, whilst on the mountains only at angle of about 60°. — It is impossible to reconcile these facts; the upheaval of the white bands must cause the cleavage to dip at a higher angle to the SSW, that is either vertically or to NNE. —

Putting these aside, the planes of stratification, which in themselves obscure, are rendered more so by those of fissure; it will be the more necessary to find out the original position of the cleavage plates. — Were they horizontal? if we grant this, there is an easy explanation for the parallelism of their direction, when inclined, with the line of upheaval. — On the other hand

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Cleavage
strata were once horizontal, consequently 15 leagues thick? In the southern part of Navarin Island which is only hilly, we find on the East & West coast & in a line of direction of cleavage. the clay slate either truly vertical or dipping at very great angle to SSW or opposite point of compass. In all probability the same position of cleavage extends across the island. a distance of 39 miles; N & S in width I know on both sides it is at least 8 miles. — can it be believed that extensive tracts of country nearly 3 leagues wide have been upturned through an angle of 90°, or near it, & that the direction of the planes in the rock should never vary more than one point. — that the rock should show signs of no violence, that the country should not present reg ridges & abrupt precipices? Yet this at must all be granted if the planes of cleavage were originally horizontal. It may be here mentioned, that in the same site & on both coasts on proceeding from the North to the South, the following order of dip is met with; first SSW. then N by E & lastly vertical; if we suppose the inclination to rise from upheaval, this order does away with any regular cause; the SSW dip must become vertical before dipping to N by E, which is not the case on either side of the Island. —

were the planes of cleavage originally inclined at a high angle or vertical? Every argument against horizontality, in direct proportion to the uniformity & greatness of the observed dip, will

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forcibly apply in favor of this view. —

All exceptions to uniformity may be explained by disturbing forces, & as the inclination is generally so great. it will be certainly with much more probability than if they had originally been horizontal. —

We have shown on a foregoing point, that there is a coincidence in form of Land & direction of cleavage in this country; likewise the excessive improbability that this should occur, if the planes of cleavage originally had any position excepting the horizontal. (B) — We must therefore conclude, either that the cleavage was horizontal, or not being so that the chain of mountains (& hence form of land) was not raised by a line of elevation; (a)

Against the former of these two suppositions strong arguments have been brought forward. — I will therefore state the hypothesis which the above data would lead to; disregarding however monstrous & unlikely it may be. —

It is; that during the consolidation of the rocks of Tierra del Fuego. — a fissile structure was impressed on them. which had a WNW & ESE direction; & that the dip was generally at a high angle to the SSW; perhaps the same amount of inclination was not universal, but whether how much to attribute of the differences to this cause. & how much to subsequent disturbances (the Trappean rocks afford evidence that there have been some) I am know not. —

2d — that in the same direction as cleavage, gr mineralogical changes took place in the

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(a) I do not mean that the land has not been elevated; but that there has not been lines of upheaval. which throwing the strata on each side, has formed mountain ridges. —

(B) From the observation I now consider it as established that there is some physical connection between. lines of Elevation. metamorphic action & cleavage. If we deny this & the possibility of a mere chance coincidence, then all the "monstrous" conclusions will serve as ad absurdum arguments. —

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nature of the rock. — on a small scale I have endeavoured to show this in the clay slate of Ponsonby Sound. — On a great one, we see it in the northern arm of the Beagle channel, which running WNW & ESE separates the grand mica slate ridge from the an escarpement precipice of clay-slate. — 3d that here the chains of mountains have been formed, by the different degrees of rapidity of weathering, continued during a succession of ages; that in those lines of mineralogical change, the more enduring kind has formed the ridges. — I am aware what overwhelming arguments can be brought against the conjecture: analogy from other mountain chains. where stratification may be evident. &c &c &c. And in this very instance, from the neighbourhead continuation & direction of the volcanic line of the Andes, there is a presumption that their mountains were upheaved by a like agency. — It must be recollected however that the nearest volcano is probably 600 miles distant & that in the southern part the line is intersected by deep sounds & is much bent from North & South direction of the Andes. — I have only mentioned this hypothesis, to show the tendency of the facts. which I have collected in the geology of Tierra del F. — That the data may be imperfect (a) or reasonably insufficient is too probable. — The study of the slate rocks in the St. of Magellan may perhaps help to clear up some of the doubts & remove some of the contradiction: —

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(a) Whether it should ultimately turn out, that there is a parallelism between direction of cleavage & line of elevation. or not; yet observations on its direction will show in any country whether one cause is common to it or that there is some change. It appears to me an accurate study of the direction of cleavage as connected with the form of mountain chains will help much to understand the nature of both. —

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Fissures are parallel smooth divisions cutting the rock generally at a high angle. There may be more than one set present at the same time. — Their occurrence is very general. — The origin & nature of these seams is perhaps not analogous to columnar structure. (a) — In the crystalline feldspathic rock & greenstone, it is sometimes almost difficult. under which term to describe. — The following set of observations were made in the clay-slate of Navarin Island, NE, end of Navarin Island.

Jan 19th
Cleavage, dips to SSW angle about 80°
∴ Angle of intersection between —— runs WNW & ESE
direction of planes of cleavage Fissures dip about same angle
& Fissure = 45° — run WSW & ENE

Jan 21s
N. shore of Beagle Channel. Cleavage dips SSW about 10°
opposite centre of Navarin Isd —— runs WNW & ESE
Angle of intersec: = 78.75 Fissures run N by E & S by W

East entrance of Ponsonby Cleavage dips S by W angle 50°
Sound. Angle of intersec: — runs W by N & E by S
1st set = 45° 1 Fissures dip NW by N. angle 45°
2d set — 84°.125 — run SW by W & NE by E
Both sets occurring together 2 Fissures dip E by S 1/2 S angle 87°
— run N by E 1/2 E & S by W 1/2 W.

Feb: 6th
East shore of Ponsonby Sound Cleavage dips vertically
Angle of intersec: = 78.75. — —— runs WNW & ESE
Fissures dip NW by W angle 65°
—— run SW by S & NE by N

It is remarkable that out of these 5 five cases of intersection, that two of the angle. 45° & 78°.75, 79° should each occur twice; it gives ground to conjecture there is some general law. — I record these few & imperfect observations, — but there is need of many more. —

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Alluvium
There yet remains to be described the remnants of a grand alluvial formation & some facts connected with this subject. — The South & SE parts of Navarin Island are surrounded by a belt of a table land. — it forms perpendicular cliffs of about 60 feet high on the beach; is of a pale colour; & is composed of a sandy clay, in which great numbers of rounded stones are imbedded. — These stones vary in size from a pebble to a large Boulder & are composed of many different rocks. — Chiefly slates. & many varieties of greenstone; feldspathic rock with angular fragments of slate; quartz, porphyry; granite & syenite. There was no signs in any horizontal arrangement of the larger blocks to show regular deposition. — A Debacle sweeping along. has been arrested in its course. — Similar cliffs occur on East coast of Navarin Island. —

Within the Beagle channel, this alluvial formation is perhaps best seen, we have here banks & cliffs of the height & colour described. & which on both sides exactly correspond. — It is only necessary to behold these to be convinced they were once united; this is almost proved at its furthest point West, by the occurrence of a head-land of alluvium which stretches half across the channel & which geologically with respect to the bordering slate mountains may be considered as an island, which has been left, when the neighbouring parts were removed. In this one place I saw traces of horizontal deposition, (a) — In Picton & New island there are opposite & corresponding cliffs & shoals

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(a) 1834. Feb: The lower part is very white & apparently sandy: Cliffs estimated at 200 ft high (like East coast of T. del Fuego; it contained grand beds following the inequalities of the other.

(b) The Detritus was here earthy contained but few small stones. these being angular rounded. —

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Alluvium
water in a line between them. They occur at Cape St Rio & in north part of Wollaston Isd. — From the similarity of all these cliffs; & from their being present within an imaginary figure drawn through the extreme points. I think it certain that an alluvial plain once connected them. The sea & weather is even now reducing the remaining vestiges; it is therefore impossible to say what its former limits were; the extreme points of its present occurrence are distant in Latitude 45' miles. in Long: about 50'. the area almost 40 miles across. In the NW part of Wollaston island I was surprised to see on the beach great boulders of rocks different from the neighbouring ones; Some miles distant. in a more sheltered place I afterwards saw the white cliffs & then understood the presence of the boulders, as monuments of the alluvial plain. — Large stones must easily be carried on in the mass of a debacle, possibly in other cases, besides this, their isolated occurrence may be explained on a similar principle. —

In Navarin Isd, (a) we find Guanaco. foxes & Mice; it is highly probable that these animals passed over from the mainland, before the Beagle channel had broken through the bed of Alluvium. —

In Wollaston Isd I saw the skull of a Guanaco on the beach. but not much rotted; was it brought over by the Fuegians? or is it an inhabitant? thus by the wasting of a few more centuries or even less time, we might have had islands where animals lived & where boulders of foreign rock were lying on the beach, & the presence of each equally inexplicable excepting by vague conjectures. — (B)

the area almost 40 miles across] added pencil in margin.

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(a) It is very remarkable that J. Button says there are no Foxes or Guanacos in Hoste Island, which in every way appears equally well adapted for them. — I found however one mouse! —

V E. Coast of T. del Fuego for paper about this Diluvium. —

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Alluvium
From the rounded state of most of the stones & the proportion clay in the alluvium, it must have existed in this state previous to its transportation. — I think from the mineralogical nature of the rock the debacle must have flowed from the westward. — I can only account for the present situation of the cliffs by supposing subsequent to their deposition some change of level in the country, probably a sinking rising — I think so, from not believing that any body of alluvial matter pushing amongst the islands as now situated, would form so continuous a field, as must have once connected them. — We have evidence of some great disturbances, either aqueous or terrestrial: — on an isolated hill in Hardy Peninsula (P 21 (a)), at least 400 feet high. & composed of a peculiar rock, fragments of different varieties of greenstone were lying; also, on the sides of Beagle channel there were pebbles. which could not have been brought by brooks, at an elevation of about 150 feet. —

Since this supposed change of level the sea has continually been effacing all signs of the debacle; the cliffs only now remain, where they are sheltered from the prevailing westerly winds & waves; here they are partially protected by a covering of coarse grass & by a shingle beach at the base. —

The formation of the Beagle channel. which stretches across the country, with an average breadth under two miles, in a nearly straight East & West line for a distance of 120 miles (a), is very problematical:

21] added pencil.

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(a) Capt. King states, the length to ar 120 miles & so straight that no points of the opposite shore cross & inter[illeg] a free view through. — & that its average breadth is not more than a mile: ? Geog: of Tierra de F. P 16. —

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Alluvium
In its course it is bounded on each side by a succession of rocks. — On the East. cliffs of Alluvium; then clay slate; clay slate & micaceous schists; clay slate & lastly crystalline granitic rocks. — From this cause & from not running parallel to the ridges, it cannot be considered as an original valley. — it is a valley in a certain sense, in as much as its whole course is bounded by mountains. —

There are no particular signs of violence in the rocks; excepting indeed in the entrance of Ponsonby Sound (V Fig 2), where the junction of the two waters probably owes its existence to the shattered condition of the mountain. — I observe the line of the channel, is nearly the same, as the termination of the main-land from Cape St. Rio to Cape Good Success: may we imagine an E & W line of change of force, which has at any time altered the level of the land. — As soon as any communication of the water of the two seas took place; I can believe currents stronger, than now exist might help to excavate its channel. — For the reason given at (P 5) I do not think the sea would have much influence, excepting in the above-mentioned manner. —

Glaciers
When sailing through the Beagle channel. I often noticed the great difference of structure in the tongue of land formed by mountain torrents & by glaciers. — in the former case it is a bank of pebbles; but with the glacier it is a pile of enormous

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Form of land & quadrupeds show subsidence though perhaps read elevation —

Soundings off Christmas Sound R. N. p. 140

Globular Porphyry. Daubuisson p. 108 311

Angle of cleavage in clay slate Daubuisson vol II p. 101

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Glacier
boulders. — many of them several tuns in weight. — The Glaciers form a perpendicular cliff of the clear ice to the sea; (when I was there it was the thawing season), a torrent, which runs & may be heard roaring, behind the vertical face, drains the upper parts. — Large masses of ice are continually falling into the water, so that in the Beagle Channel we had a miniature of the icebergs of the Antarctic seas; & as the cliff continues perpendicular, it is evident the whole body must be gradually descending. — the numerous fissures & the rolling noises heard by night afford evidence of the same thing. — By this action large fragments of rock must be torn off & in the torrent & under the glacier. must be dashed together & thus rounded. — V Journal Occasionally avalanches fall. which raising a great wave washes away all lesser bodies, but only removes the boulders to some distance, & thus in some places, they extend for a considerable space from the shore. — The glacier, which I am able to approach nearest to came down to the sea in a cove. one side of which was mica slate. the other terminated by a promontory built up of enormous boulders. — it must at least have been 60 feet high & of considerable breadth. — One of the blocks of granite which was on the beach was of an oblong figure & averaging 6 feet above the sand. how much below. I cannot tell, & 30 yards in circumference. — When this promontory was formed (a), the glacier must have had another direction.

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(a) If the excavation of the Beagle Channel is curious, it is equally so, that the quantity of matter annually brought down by the glaciers & mountain torrents has not long since filled it up. — The clearing out by a body of water of such a channel. with its pebbles. boulders & mud. & the subsequent depositing of it in the vallies of a neighbouring country. would explain create the formation of Alluvium. similar to the one described. — N.B: Pebbles were found high up on the sides of the channel. —

The N & S. part of St of Magellan which intersects in front of P. Famine the great slate band is also very inexplicable. —

NB Capt King remarks about Islands appearing where greenstone occurs is exemplified in Beagle Channel. — (it is proof of irregular form of land) —

NB. Information from Capt. Brisbane. South Desolation said to be volcanic with hot springs. — All the South Shetland with hot springs & vesicular lava, also Captain Weddell saw smoke fuming from a rock. — South Orkneys volcanic products. —

NB. Capt Cook entering Christmas Sound found the following soundings 37: 50: 60: 170: a deepening of at least 798 feet.

Georgia is mentioned by Forster?? Slate Rock

C7 b iii a

Georgia is ... C7 b iii a] 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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