RECORD: Darwin, C. R. [Essay on] Cleavage. [5.1836] CUL-DAR41.59-77 Transcribed by Kees Rookmaaker and edited by John van Wyhe (Darwin Online, http://darwin-online.org.uk/)
REVISION HISTORY: Transcribed by Kees Rookmaaker, corrected and edited by John van Wyhe, corrections by Gordon Chancellor 9-10.2011. RN2
NOTE: This is one of several "synthetic essays", as they were termed by Sandra Herbert, written by Darwin near the end of the Beagle voyage. Some of this discussion of cleavage was incorporated in South America, chapter 6 and ' On the geology of the Falkland Islands' Text. See Sandra Herbert, 1991. Charles Darwin as a prospective geological author. British Journal for the History of Science 24: 159-192. Text. Sulloway 1983 dated this essay to May 1836. As the post-voyage dates of some of the references cited make clear, especially on the versos, Darwin continued to work on this document after the Beagle voyage ended in October 1836.
The essay is written mostly in ink. Where pencil was used instead this is noted in the textual notes. 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.
By the term Stratification I mean those planes of division, (resulting from
some changes of circumstances,) which occur in matter, that has been deposited beneath the sea water & which particles matter was successively arranged in an undisturbed manner by the attraction of Gravity. —
By cleavage, a fissile structure. — The laminae not being necessarily parallel to the plane of Stratification. —
By fissures, planes which are seen in laminated Stratified & non-Stratified rocks: — These when they occur in the two first cases are recognized as of a different nature. In the unstratified form a similarity in appearance are believed to be such. —
Daubuisson. p. 297. vol I1
(proof of arrangement in crystals of granite. p. 308
Excellent Discussion on cleavage
New schistose structure in granite
A p. 25 like Henslow Anglesea1
Hopkins paper must be studied2
Study Sedgwicks paper on cleavage Geolog. Transacts3
Insist on cleavage in phonolite
Scrope p. 196 parallelism of axis of eruption and strata of gneiss4
Scrope's theory of volcanos p. 199
Lyell vol II p 326 on mountain chains parallel to magnetic curves5
In Brittany NW & SE direction of primitive rocks
In the Harbing cleavage at ┴° to line of mountains and granite general SE dip. WSW & ENE line common to France and Belgium. De la Beche Transl. of An. of M. p. 2676
Humboldt p. 35 Fragmens asiatiques general NW line in N. Hemisphere7
at Caraccas layers? of limestone in gneiss
Pen-ham vol III ??
Capt. Allardyce in Madras Journal October 18368 states that general direction of hills NE & SW, that Ghauts have intersected this by N & S line of fracture. — granite on west coast from Surat to C. Cormorin. — In southern India scarcely a trace of aqueous deposits. — Cranitic granite plains remarkable level. —
Compare with America
1 Notebook A, p. 25e.
2 Possibly Hopkins 1836.
4 Scrope 1825.
5 Lyell 1837, vol. 2, p. 326.
In my geological account of each district I have described all the facts respecting the
mere cleavage & stratification of the rocks & likewise the more obvious conclusions which might be drawn in each particular case. — I will now take a general review of the whole phenomenon as seen in S.America. — Humboldt has discussed this subject of "Loxodromism" in vol VI p 591 of his Pers: Narrative.1 — That my observations may be thought more worthy of attention, as not being warped by the influence of so great a name; I may venture to mention that this part of the work had been so entirely overlooked by me, that I had copied out all the notices on the subject, scattered through the previous volumes. — I have delineated by red lines on a map, the dimensions, with the horizon of the cleavage where I have been alone to ascertain them. — To begin with the North-Eastern part.
1 Humboldt 1819-1829, vol. 6, p. 591.
(a) The word "Loxodromism" must mean (from λοχοα oblique) I suppose an
obli inclined direction? I have used it rather in the sense of parallelism of direction alone in contradiction to a real parallelism, between any two strata. — or does it mean, a certain fixed direction or angle with the meridian in different places?
M. Reboul Journ. de Physique 1822. Decemb. p. 245 on cleavage1
Thünberg says mountains at C. of Good Hope all range NW & SE2
Symetry in curved lines of Panama, West Indies, Tierra del Fuego - East Indies. Chinese coast. Aleutras isles. —
Lyell says vol III p 132 in St Eustacia (W Indies) recent coral rock elevated 1500 ft dip SW ∠ 45°3
"Santiago Note book" p. 29 and 30 31 speculations4
As Lyell urges irregular passages of granite into gneiss great perplexity: why so we know phonolites (& basalts) become slaty from crystals of felspar placed in the direction, why not those of mica in granite — it would become gneiss —
Consult Dr Fitton's paper at length5
1 Darwin seems to have copied this reference from Humboldt 1819-1829, vol. 6, p. 593.
3 Lyell 1830-3, 3: 133.
4 Santiago notebook, pp. 119-121.
5 William Henry Fitton was the author of the geological appendix to King 1827.
Humboldt P 594 vol VI states that "Venezuela is one of the countries in which the paralellism of the strata of gneiss granite, mica slate & clay slate is most strongly marked. The general direction of these strata is N. 50 E & the general inclination from 60° to 70° North West. Thus I recognized them on a length of
shore of more than an 100 leagues, in the chain of the shore of *Venezuela, in the stratified granite of las Trinchacos &c &c &c. The inclination to the NW are again The same direction NE & SW & this inclination to the NW, are again observed, although less decidedly in the limestone of Cumanacoa, at Cuchivans, & between Gianaguana & Caripe. — The exceptions to the general law are extremely rare in the gneiss granite of the Cordillera of the shore; it may even be affirmed, that the inverse direction (from SE to NW) often bears with it the inclination towards the SW.
As that part of the group of the Sierra Parime, which I passed over, contains much more granite, than gneiss, on other rocks [this Humboldt quotation is continued on the page 60a]
Sierra Parime extend N. 85° W. line (not introduced). Humb. VI. P. 503 & 519 & 527
Consult the whole of VI volume
Symmetry in world. RN p. 382
RN. p. 41 speculations on
wor currents in world
line of mountains show area of elevation are of propelled heated rock. — cleavage likewise shows area of heated rock, if WNW in northern hemisphere
does is precedent (as Lyell sometimes says), then the streams in such, [see] if movement will not agree. —
Daubuisson vol II on layers of lime in granite p. 6 do p. 433
why are there not primitive calcareous sandstones p.8
Character of mica slate p. 80, difference from phyllade (important) p 95 and 96
cleavage p. 100 & 101
passage of limestone into clay slate p. 109
ditto p. 189
1 Humboldt 1819-1829, vol. 6, p. 594-5.
2 Red notebook, p. 38.
distinctly stratified the direction of the layers could be observed in this group, only on a small number of points; but I was often struck in this
country region, with the constancy of the phenomenon of loxodromism. The amphibolic slates of Angostura run N 45 E, like the gneiss of "Guapasoso" & "like the mica slate of the peninsula of Araya, although there is a distance of 160 leagues, between the limits of those rocks. — The direction of the strata of which we have related the prodigious uniformity is not entirely parallel with the longitudinal axes of the two chains of the shore & of Parime." "Can it be admitted (a) that the direction of the Eastern Cordillera of New Grenada, which is nearly N 45 E, from Santa Fe de Bogotà to beyond Sierra Nevada de Merida & of which the chain of the shore is but a continuation has had an influence &c the direction (hour 3 & 4) of the strata
(a) The micaceous schist of Andes of Quindice & Alto de los Robbes,
near in Popajan, run N 60° E. — therefore nearly parallel to to the Eastern branch of the Cordilleras P 168. Humb. — Superpos. —
Also quartz rock,
directed N to dip to SE (?)
at Aroma. Magdalena & Cascas. V. Humb. Super. P 29[illeg]
in Venezuela"?1 a1. a2 (a)
From what I have seen of similar formations, these I can feel no doubt that the strata planes of (so called) stratification in the gneiss — granite. mica slate &c are parallel with the laminae of those slaty rocks. Indeed the expressions, "direction of the layers" would almost point out this identity. —
We next proceed to Brazil. At Bahia, where the constitution of the rocks appears to be very similar to that of Columbia & Guyana, the direction of the
strata layers is N 34 E & the dip to the NW. ؟؟ — I use the term strata here, as Humboldt has it. At Rio de Janeiro, the direction is subject to much variation. NE & SW is nearly the mean the most prevalent. — Both here & at Bahia mineralogical changes in nature, such as from mica slate to gneiss tale place in places identical with the fissile structure as appears from Humboldts description to take place to the North. —
The hills in this neighbourhead, & the Sierra dos Orgars & the valley of the R. San Francisco run in an ENE North & WSW line.
The coast likewise has here the universal direction of E by North. South of R. de Janeiro, Spix Vol I 289 met a second chain of hills2
1 Humboldt 1819-1829, vol. 6, p. 594-6.
2 Spix 1824.
(a2) These planes of stratification are identical with the cleavage. Humboldt vol VI P 99 states that this direction is common to the gneiss — granite — mica & hornblende slates & likewise (but not so commonly) to the secondary ranges. — The mica & clay slates contain layers of native alum, graphite, chloritic & [illeg] slates & slaty amphibol.
(a1) In the Caribbean sea, 20 miles north of the shores of Caraccas, Humboldt saw layers of gneiss inclined to the NW. — & therefore running NE & SW. — Vol VI P 805. —
running NW & SE; but the direction of the "mountain masses" & an evident transition from gneiss into mica slate, was NE & SW or at right angles to the hills. —
The third chain which divides the provinces of Rio & S. Paulo, I imagine from the description must like wise have a NW direction P 291, but
the a cleavage nearly at right angles. — At Ypanemia South SSW of S. Paulo, there is a "dirty lavender-blue primitive clay slate" vol II P 52, which runs from East to West.
M. Spix travelled to Villa Rica, in the road south of St João del Rey P. 136 at Corriego dos Pinheros he met with [elastic] mica slate cleaving NE & SW, angle 60-70. This was at the foot of the Sierra Branca "on our left we had the mountain of Capivary on our right the Sierra de Ingahy, both of which run parallel with the Sierra Branca from SSW & SW to NNW & NE; & all branch out almost at right angles from the Sierra de Mantequeira, the main stem
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of the mountains in Minias."1 Hence this last main chain runs NW & SE. P.197 —
Again the Sierra do S José runs NE & SW as do the neighbouring strata of granite & talc-mica slate. P 154.
which Further on, north of Morri de Solidade taleaceous slate, which appears intimately connected with the formations of V. Rica P. 156, has a direction of NW & SE. Again some leagues to the North, the Sierra de Oiro. Branco P. 158 & its stratification runs WNW & ESE. The Morro de Villa Rica runs E & W (Spix & Caldcleugh2) P. 185 appears to have been formerly connected with Ita columns. Caldcleugh vol. II. 258. In the latter mountain, the cleavage W 15 N & E 15 S. —
In Villa Rica, Spix gives NE & SW, whilst Caldcleugh says only a little to the northward of East. — Taking into consideration all the above statements, it appears that these two distinct systems of hills, each with their corresponding cleavage, which run nearly in the two directions of (NE & SW) & (a) (NW & SE). and that these intersect each other at large angles. — I imagine the confusion in the cleavage near the city of Rio & the unusual direction
1 Spix 1824, 2: 137.
2 Caldcleugh 1825. (Full text available on Darwin Online)
(a) This latter direction commonly inclines to W & E.
of the coast-line, are consequences of this fact. (a) — Humboldt vol VI P 597 in a note says, "According to the Mss. notes of M. de'Eschwege & his Geogr. Gemalde von Brasilien P 6. The strata of the primitive & intermediary rocks of Brazil run very regularly, like the Cordilleras of Villa Rica (Sierra do Espinnaco) N 28 E. — The inclination of the strata is generally towards ESE." —
I cannot reconcile these differences;
perhaps [illeg] His direction of agrees with one of the systems for does not differ much from the more prevailing system of NE, although he does not notice those line, which more nearly run East & West, & probably is the result of observations extended over a greater part of Brazil. — (Certainly of far most weight)
(R. Plata) proceeding to the South, we come to the northern shores of the R. Plata. At Maldonado granitic & slaty quartz rocks, run with great constancy NNE & SSW. — Their laminae are very highly inclined. — This direction is common to the hills. — one chain of which certainly extends far to the North of the Plata & I am told reaches to Southern Brazil. Near Las
(a) M. Esch—
describes attributes it to the approximation of the two lines of mountains, that the coast & that of Villaria, which are said generally to run parallel & in a northerly direction. —
cleavage (R. Plata) 9
Minas this system of hills appears to be crossed by a broard band of blue siliceous clay slates, of which the cleavage, although much confused, runs somewhere about E & W. In places I describe, a confused mass of mountains, the cleavage following no determinate direction, but in each
ridge spot parallel to it the line of its own hills. —
beyond some distance to the North, to that another E & W line of hills joins the first system.
In the country round, M. Video & 80 miles to the West of it, at Colonia del Sacramiento all the rocks cleave within a point of E & W. —
The To this large district, belongs the clay-slate hills of las Minas. — We shall subsequently show that South of the Plata, there are other lines of hills, belonging to this system. — Hence we see two A on the Atlantic side of this province, an extensive NNE system, which to the West is [illeg] joined by & intersected by a large angle, by the E & W rocks divided into East & West laminae. — In the. Throughout both these systems, frequent mineralogical changes (granitic rocks, to limestone, hornblende, clay slates &c) take
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cleavage (R. Plata) 10
place in planes identical with those of cleavage. — In the Province of Entre Rios on the banks of the Uruguay, I heard of a northerly line of low granite hills. Mr Miers1 states that at Barranquitos ([blank] leagues East of San Luis) mica slate dip at an angle of 45° to the SE & therefore runs NE & SW. — To the South of a line connecting the three above mentioned districts, I do not know of any rocks belonging to the NE & SW system. —
V. Geology of Brazil. Any person having read the works of Humboldt,
to the various descriptions of Brazil, & the few notes which I have added to those parts & the Provinces of La Plata, will recognize a general similarity in the formations nature of the rocks, which compose the great Eastern protuberance of S. America. — I conceive the country is sufficiently known, to pronounce, that in at least in the neighbourhead of the coasts, no other great & distinct formation is found: there is much probability
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judging from the section in the latitude of the Plata & from the structure of the northern & N. Eastern coast, that one formation extends over the whole area to near the Cordilleras on its western limits. — But whether
or not, the rocks are similar & belong to one group, or whether they are not, we recognize in the whole a most astonishing "Loxodromism". —
Venezuela. Sierra Parime &c &c. (Humboldt) N 50 E
Bahia. (north Brazil) (Darwin) N 34 E } of little value
Rio de Janeiro. (near the city) ( do) N 45 E }
Southern Brazil (Spix) N 45 E } Intersection
Near Villarica (Spix), A (WNW or NW) & (ESE or SE)
Brazil (generally) (Eschwege) N 28 E
NE shores of La Plata (Darwin) N 23 E }do
nea Country of M. Video. A (W & E) system
[sketch] N 23° 50° E S 23° 50° W
We here see in places so remotely apart,
one a prevalent direction, the extreme variation of which only amounts to 27° degrees, that is 1/6.6 of the semicircle of the horizon. In two districts we meet with a second & distinct system of cleavage, & in both cases, the angle of intersection is large & nearly
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the same. — I cannot pretend to conjecture whether these changes in direction point out differences in age of the formations.
Universally I believe the inclination of the laminae to be great: it more frequently exceeds, than is under the angle of 45°. —
The remark of Humboldt, that this high inclination by no means is necessarily accompanied by mountainous land, is illustrated with great force by the monotonous level savannah of the North shore of La Plata. —
The point of dip is not nearly so constant as that of the direction of the strata. In Venezuela Humboldt remarks that
SW NW is the most common. — In Brazil ESE. —
In La Plata, I do not feel sufficiently certain to make any statement. (a) I have already repeatedly urged, that this uniformity in
of direction does not only apply to the cleavage of slaty rocks, but likewise to the separation of very various mineral substances into what would commonly be called strata. (a) —
Justly to appreciate the importance of this subject, it is necessary to bear in mind, that the Area, of which we are speaking,
(a) With respect to the figure of the land; from the R. Plata to the North of Brazil, there is a
toleb tolerably exact parallelism, between the direction of the laminae, the mountain chains & coast line. — In Venezuela the NE & SW system is bounded by the parallel Cordillera of Merida. — To the North however, the strata are truncated by the S Atlantic & Caribean seas. — To the W & SW the line of Andes destroy all idea of Symetry. —
extends from 12° north, nearly to 35° South latitude; a space of 2800 miles. —
Conclusions drawn from so vast a territory become at once applicable to the geology of the whole globe. —
In the vast plains, which bordering the Atlantic extend South of the Plata, for the first 300 miles of latitude, a few ridges of older rocks, protrude through the level surface. All these will be seen to belong to the same system, as the country of M. Video.
First we may observe in the maps, a low line of hills, called La Cerrillada, which run W. 27° N. (a) A hundred miles to the South of this, is the Sierra Vulcan, which beginning at Cape Corrientes runs in W 15 N line. — This ridge, which from its level outline is very remarkable, is composed on an amorphous quartz rock. it extends probably
[illeg] 150 miles;
Again 60 miles further Southward, we meet the Sierra Guitru-guegù, composed of feldspathic rocks & clay slates. A mass of hills, having
(a) These bearings can only be depended on in such poor maps to within a point or even more. —
cleavage N. Patagonia 14
a general NW & SE direction, make up a mamillated country, which reaches southward 25 miles to the foot of S. Ventana. — The cleavage however of the clay slates, where best developed, was directed W 35° N. with a southerly dip. —
The S. Ventana attains an elevation of
nearly 4000 3200 ft & is, I believe, on this Eastern side, one of the principal mountains, which can be found between T. del Fuego & the South part of Brazil. —
(Lat: 31 S) 38°.11'.50" Long. 61°.56'.33" height 3200
It is composed of a hard quartz rock, divided into thin strata, or almost laminated. — These strata,
dip have a direction of W 35 N, & dip to the SW at angle of 45° & upwards. — The mountain is very narrow; its highest & central part of the ridge extends NW & SE; but towards the Eastern extremity the line is W 25° N., as likewise I suspect is the western prolongation, which I am told is found 20-30 leagues distant.
The main chain is bordered by a few lines of detached hills, which
are run in parallel direction. — To the South, the eye wanders over the unbroken plains of B. Blanca. —
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cleavage N. Patagonia 15
Between B. Blanca & the R. Colorado, there is a remarkable ridge composed of the modern calcareous rock, which runs W. 15° N. for a considerable distance. — I have given my reasons, for
supposing conjecturing that there is an underlying axis of hard rock. — Some Gauchos moreover told one, that far in the interior between the rivers Colorado & Negro, there is a mountainous country, composed of very hard grey (quartz?) rocks; the hills having somewhere about an East & West course.
Thus we see in the country included between the rivers Plata & negro, everywhere the few ridges have the line of their bearing, between W 15° & W 45° North. The cleavage, where
visible distinguishable, ranges within these limits. Beholding the S. Ventana, rising in the greater part of its circuit, from a dead level perfectly smooth plain, I was forcibly struck with this, as an example of coincidence, between the line of elevation & the cleavage of the rock in that territory. —
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cleavage N. Patagonia 16
South of the R. Negro, on the eastern coast, I know of no line of ridges, till we enter T. del Fuego.
I will however first begin with the Falkland Isds situated nearly in the same latitude.
In these Islands the mineralogical nature of the rocks is characterized by much simplicity,
as whilst their mechanical structure is both complicated & extraordinary. The direction, W 15° N, is generally common, to the nearly vertical laminae of clay slate, to the inclined strata of quartz rock, to the lines of principal hills, & to the general configuration of the land. —
From what I understand of the geology, the ranges of quartz rock, appear to point out lines of metamorphic action. — Where the
common ordinary direction varys (a). the same variation appears to happen occur in all the above phenomena. — (b)
The facts however,
which are of most interest are those which would seem to indicate, that the force, which has arranged the vertical
(a) (very seldom more than two points)
(b) The angle of inclination is much greater in the slates, than in the quartz rock; The point of dip is either S by W or N by E, perhaps the former is the most common
cleavage Falkland Isd 17
laminae, is an antagonist power to ordinary gravity. — I allude to the same kind of sandstone, occurring first as an horizontal stratum between masses of vertically laminated clay-slate; secondly as parallel layers, mingled with the clay slate, & the whole retaining the common direction; & thirdly as one & the same stratum, affording at its two extremities, instances of
the both the foregoing structures. —
T. del Fuego
We now come to Tierra del Fuego. — I include under this name, all the land South of a line, joining the opposite mouths of the Sts of Magellan. — In space, although not in quantity of land, this may be roughly described, as equal to Scotland. — In the promontory at the SE extremity the cleavage runs W (even with a little Southing) & E. — In this direction lies, the lengthened Isld of Staten land. —
With this exception, there is a most remarkable uniformity, over the whole southern part T. del Fuego: everywhere the clay slate, the mica
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cleavage T. del Fuego 18
slate, & their line of junction run
WNW & SSE W 23 N, dipping almost universally to SSW at high, but varying angle. — Parallel to this line, runs the outer coast & the grand chain of mountains, (the nucleus of which I believe is granite), which includes Mt Sarmiento 6100 ft. Mt Darwin 7000. Chain Mt 4.300 &c &c. — In the northern division near Port Famine, all the clay slate is directed within a point of N. W. 40° N. as before, the outer coast is parallel to this line & the granitic land, of South Desolation. As before, parallel to this, is the line of outer coast, & that of the separation of slate from tertiary formations, the granitic land of S. Desolation, & lastly several of the channels. In this last respect the parallelism is very striking. Capt King (Transac: of Geograph: Soc) says, "The uniform direction of the headlands of the North shore of this Island. (S. Desolation) is remarkable. Upon taking a set of angles, with a theodolite placed upon the extremity of the West end of Bell bay opposite to C. Holland, the most prominent points to the South East, as far as could be seen were all visible in the field of the telescope
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cleavage T. del Fuego 19
at the same bearing. The same thing occurred on the opposite shore of the Strait, where the projections of C. Gallant, C. Holland & C. Froward are in the same line of bearing; so that a parallel ruler placed on the mao,
on the upon the projecting points of the South shore, extended across, will also touch the headlands of the opposite coast."1 — Looking a short way to the the North, of the Sts of Magellan we see the same direction developed in the forms & channels of Queen Adelaides archipelago. — Considering the different parts of the whole country, it is impossible not to be struck with this parallelism, between the cleavage of the slates, the lines of metamorphic action (& consequent changes of formation); the principal lines of mountain chain & the general configuration of the land. In each such part there is a truly surprising Loxodromism; but in the different parts, the variation is considerable, amounting from W 0° N to W 40° N. The curved band of mountains which here terminates S. America, exactly corresponds to this progressive change in cleavage. If my points of observation had
1 King 1832b, p. 170.
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cleavage T. del Fuego 20
more numerously extended over the country, it is likely this agreement would have been more apparent. The W 40° N. system, being separated from the W & E one, by another of W 23° N, is in marked contradistinction to the sudden & total change. which is believed frequently to occur. —
In the line of the outer coast or E 40° S (about 550 miles distant to the S.) the lofty volcanic group of the Shetland Isds is situated. — In the (؟) Government charts the line of Islands runs about W 40 North & E 40 S: whilst in the Adelaides Isd, it is W. 23° N &c. —
In a like manner the distant Isd of Georgia, composed according to Forster (Observ round the World I)1 of clay slate, has its longer axis directed nearly at W 40° N. —
I think there can be little doubt, but that, T. del Fuego & the Falklands (although 450 miles apart) belong to one system, or, that the near approximation to Loxodromism in the cleavage of the caves, is not accidental.
I suspect also, that the Shetlands & Georgia are likewise parts of the same system.
1 Forster 1778, p. 12.
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cleavage T. del Fuego 21
Between this most southern part of America & the district N & S of the Plata, there is a space of more than 700 miles, where the older rocks are concealed by Tertiary deposits. — I must however except some porphyries, where no structure is developed & a patch of quartz rocks, similar to those of the Falklands.
Does not this help to show, that the connection
indi of those two great systems, indicated by their near Loxodromism, is valid? Is the quartz rock of the S. Ventana, dipping towards S 35° W, connected by some law to that of the Falklands, which dips to S. 11° W? I think so & go still further: for I suspect, that the rocks of the Plata (especially the granite & clay slates on the northern shore) are again connected with the transverse system of the interior of Brazil. —
To return to T. del Fuego; north of the Adelaide Archipelago, which has, as before shown, a direction common with the west part of the Sts of Magellan, we see the coast line, channels & main Cordillera, suddenly assume a N & S. direction.
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Any one would be inclined to suppose that the lines of cleavage, would likewise suddenly vary. — Unfortunately I am totally ignorant of the structure of the coast, for nearly five degrees of Latitude Northward. — But that this conjecture is very far from certain, we may feel assured, because on the shores North of C. Tres Montes, which extend even a little to the East of North, the cleavage has a universal direction of 19 degrees W of North.
Hence the cleavage in this space of five degrees, may possibly be directed in a line between the bearing W 40° N of the Stts of Magellan & that of W. 71° N of those Northern shores. —
Chonos & Chiloe Archipel.o
The basal formation from C. Tres Montes to the further extremity of Chiloe is one grand one of micaceous schists. — The distance is about 300 miles; in the whole of these is a most remarkable loxodromism, perhaps exceeding in precision all the other localities. The mean direction, within a point on either sides, is N 19° W; the dip (at angle about 45°) is far most frequently towards WSW. — This latter
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Cleavage Chonos & Chiloe Archipelo: 23
fact favors the idea, that there is a gradual change from the direction W 40° N of T.del Fuego, where the SW dip is so prevalent, to this one of W 71° N. — In layers parallel or identical with the cleavage, there happen incessant changes in the mineralogical constitution of the schists; ampelites, mica & chloritic slates repeatedly alternate. —
We may here observe an exception to what in some places would appear to be a law, namely that, whilst the cleavage is directed N 19 W. the coast line & without doubt the main chain of the Cordillera extends in a line, a little to the East of North.
Moreover there are several examples of secondary ranges of granite, of no mean elevation, which intersect the direction of the laminae at various & quite uncertain angles. —
Proceeding northward at Valdivia, the same mica slate formation is present: The strike of the
laminae cleavage is here subject to a degree of incertitude, I have never seen in any other part of S. America. Many
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cleavage Valdivia 24
of the layers appeared to follow the curvatures of great spheres. If any one direction was most prevalent, it was NW & SE. — The angle of inclination was generally small. —
In the few places where I saw the older formations at Concepciòn the same remarks, as at Valdivia, are applicable. Perhaps in both cases, the laminae of slate had originally been formed at a low angle, under which circumstance, it is manifest, all posterior disturbances must alter the [primary] direction, more considerably, than if they had been inclined. —
Central & Northern Chili
In Central & Northern Chili the proportion of laminated rock is small. In several districts from Valparaiso to Copiapò, both in the lower country & within the grand Cordilleras, a direction about N by W & S by E appeared the most common. — Perhaps in the most northern parts, the line was more truly N & S. The strata in the Cordilleras, have been broken & upraised, by numerous parallel lines of elevation, which follow the same direction.
(a) I should much like to know the direction of the cleavage in this portion of Peru & likewise on the nearly parallel coasts of the Guyanas
cleavage Chili 25
amongst the secondary ranges, many however, cross obliquely towards the shores of the Pacifick. The more important of the mineral veins, most generally, follow the same line with the cleavage & stratification.
Beyond the limits of Chili I possess no information. —
Looking at the Cordilleras & the immediate neighbouring country from C. Horn to the extreme point, where my observations end, we may observe a gradual change from a cleavage directed E & W to a system of N & S lines. Beginning at the southern extremity, we see the Cordilleras bend to WNW, NW & then assume that direction of a meridian, which it retains for so long a space. In my geology of Tierra del Fuego, I stated the WNW system appears to be in some respects distinct from the Phitonic one of the Andes. — I imagined that this latter was warped from its usual course & so constantly kept on the extreme western coast. (a) — Certain it is, that
(a) I should much like to the know the direction of the cleavage in this part of Peru & likewise on the nearly parallel coast of the Guyanas. In the interior of the continent, near the bijunction of the Orinoco & Amazon. — there is much irregularity as if from intersection of two systems. In neighbouring mountains very different stratification in each group greatest uniformity. Many of the hills East of the Cassiquia are directed NW & SE, near Esmeraldo N 70° W. &
the longest direction of. Pers. Narr. Vol VI. P. 519. 5271
It is to be remarked also that at the elbow of the Cordilleras,
near on opposite side to Arica. The NW line is prolonged in to the interior by the lofty chain of the Chiquitos. Vide. account of this grand transverse chain. Pers. Nar Vol. IV. 3032
1 Humboldt 1819-1829, vol. 6 part II.
2 Humboldt 1819-1829, vol. 4.
again, on the coast of Peru, from Arica to C. Blanco (South of the River of Guyaquil) we find another NW deflection. — Minerva, excepting on the small part of the coast from
the Guyaquil to the Isthmus of Darierus the Andes in the whole of the northern hemisphere constantly decline to the West of North. —
To complete this sketch, I may add that in a future paper (on Coral Islands), it will be attempted to be shown, that a direction in form of land between WNW & NW is common to the band of Islands of the Pacifick; also to the northern part of New Zealand, the NE coast of Australia & the greater number of Islands which front the East Indian Archipelago. To this grand system of the Pacifick, the western shores of N. America belong. This is shown by the direction of mountain ranges, the peninsula of California, the broken land in Lat 50° & chiefly by the observations of Humboldt in Mexico. He states, that in the elevated Table land, the rocks are directed from NW to SE (a), parallel to the chain of [Anaknan]: (intersect to superposition &c)
(a) To the westward of the Basin of the Pacifick, the NW system appears to encounter a NE & SW one, as seen by the chain of volcanic islands following the coast of Eastern Asia:
According to Dr Fitton (Appendix King's Australia)1 on the NW side of Australia this NE & SW direction is
found discovered in the configuration of the land obser. — Again to the West of these Eastern shores of Asia, we meet numbers of most important chains (Himalaya Korea town) directed WNW or NW, which line Humboldt remarks (Fragmens Asiatiques)2 is common to all that northern hemisphere. —
1 William Henry Fitton was the author of the geological appendix to King 1827.
Also that the clay slate of Guanaxato cleaves with great regularity in the same direction; which line ((or N 50° W) is also common to the strata of porphyries & likewise to the metallic veins of Guanaxwato, Zacatecas, tasco, & Moran (P 237) (a).
see p. 451 vol 1 On the western shores of S.America, I have pointed out two NW deflections; the southern one, of these (in T. del Fuego) I know to be parallel to the cleavage of the laminated rocks. See (a) P 26
In this part, &
a little some way to the North of it, the NW system extends across the continent. In a like manner, it would appear not improbable, that the NW system of Mexico is prolonged into the West Indian Archipelago, where many of the smaller Islands & chain of Leeward Volcanos have nearly this same direction. —
In South America, to the Eastward of the Cordilleras, I have described the grand NE system. In a corresponding position in N. America, there is a great territory, all over which according to Humboldt (Pers: Narr: VI. 596)1 a NE & SW direction prevails (b). He particularly states that Venezuela "presents a very remarkable loxodromism with the strata of mica slate,
1 Humboldt 1819-1829, vol. 6 part II.
Note (a) Humboldt states (Superposition &c P. 222)1 that on the road from Acapulco to Mexico, porphyries & coarse grained granites dip to the NW & the latter sometimes to SE. Does it hence appear probable that the two prevalent systems of the Americas intersect each other in Mexico? —
It is stated, in Cleveland's Geology of the United States,2 that the Primitive formations are generally inclined to the SE at a greater angle than 45°. —
1 Humboldt 1823, pp. 221-222.
grauwacke, & the orthoceratite limestone of of the Alleghanies & that immense extent of country (lat: 56°-68°) lately visited by Captain Franklin." (Journey to the Polar Sea. P. 529-534)1
Although there may be many irregularities & exceptions to order, I cannot look at the position of these lines over so large a portion of the globe, without imagining some unknown law has determined their symetry.
I cannot do better, before concluding this part of the subject, than copy from the Personal Narrative (VI P 592) (VI.592) the questions which Humboldt proposed to himself for every country. — I will answer each separately. (1st) Can we recognize a conformity of direction, a loxodromism of the strata comprehended in a great extent, where, are the perturbations so frequent that no law manifests itself? obscure — I think most definitely so.
(2d) Is there a simultaneous constancy in the direction & the inclination, or are the strata running NE-SW, sometimes inclined to the NW, sometimes to the SE? — Either way, but in each system, one point of the two is far most frequent.
(3d) Do the laws comprehend the formations of different ages, or may other relations of direction & inclination be observed in the primitive & secondary rock?
1 This reference is copied verbatim from Humboldt.
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[this page consists of a small paper attached at the bottom of 72a recto. 73 verso is blank]
Vol. VII. P. 50. Pers. Narr: "In travelling from Havannah to Batabano, strata of Jurassic (?) limestone were inclined at 30°-40° to the NE. — Cuba
(4th) Are not the disturbances themselves subject to certain rules, so that the partial changes of direction are most frequently 90° & lead to a total change of inclination? To neither of these latter questions can I return satisfactory answers.
(5th) Is there a parallelism between the direction of the strata & that of the nearest chain of mountains; or has that direction of strata a relation with the principal chain, or a very distant oceanic coast? To the first part of the question, such a relation very frequently, but not necessarily, exists; with respect to the principal chain & distant coast line, that relation is more doubtful. —
(6th) When we call the assemblage of rock of which the strata have the same direction a loxodromic system of rocks, & where in a vast country several of those loxodromic systems touch each other, are the changes of direction always sudden, or are there progressive passages on the limit of contiguous systems? I have adduced instances of each case. — Humboldt concludes with saying, "The same soil does not permit the traveller with the means of answering so many important questions; but the progress of positive geognosy, can only be advanced by never losing sight of the totality of the elements, on which the knowledge of the
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general structure of the globe, depends." —1
As yet we have only discussed the position & nature of the laminated rocks & direction of mountain chains. We come now to the important question of original position. I shall here only refer to the laminae & parallel strata of the older formations. It will be useless to run through all the arguments which have been adduced in each case for the original inclined position. My belief in this opinion, rests chiefly on the absolute knowledge
that gained from the Falkland's, that such is possible, & secondly, from the enormous extent, over which one direction prevails, the great thicknesses (measured in a line perpendicular to the inclination) of the inclined layers & the unbroken form of countries & absence of high ranges, where nearly vertical cleavage is commonly present. The question is the more important in the older rocks, where the cleavage & stratification, the latter being recognized by strongly marked mineralogical changes, are identical.
I am fully aware of the difficulty of understanding, on other terms, than original
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horizontal deposition from water, the presence of a thin layer of limestone, anthracite, or other substance, of which the surrounding rocks may not contain a particle. The difficulty however is common to those imbedded masses of metallic matter, called by the Germans "liegende Stocke" which are not connected with veins. — I must particularly call to mind, that in the Falklands the same power which impressed the common laminated structure, has been able to separate into inclined layers the constituents of sandstone & clay slate. (a) —
With respect to the original angle of inclination, I am induced to believe it was subject to variation; but it must be remembered that all disturbances from beneath, especially if the line should nearly coincide with that of the cleavage, must alter the angle of inclination more than the direction. I sometimes imagined I recognized a general law, that where the cleavage is not well developed, the angle is small. Certainly where quartz veins, abound to any great extent in a slate, the position of the laminae is subject to much irregularity.
Granting then that the laminae have assumed
(a) That there is considerable movement in the particles of matter after ordinary deposition, is known by the
considerable large spaces from which the concretions in the modern sandstones (for instance as at S. Cruz) have attracted the calcareous matter. —
their position from some cause distinct from subsequent angular displacement; the second question
arises is what power has so arranged the particles. — We see this structure present in rocks of aqueous origin & which betray no signs of subsequent alteration; in such cases the arrangement probably took place, some time after deposition, & before their final consolidation.
The structure also occurs, perhaps more frequently in rocks which have undergone metamorphic action. A question here arises, may not the laminated structure, always have its origin in the first stage, before metamorphosis?
I think not (a); because in coarse mica slates & gneisses the layers of quartz & feldspar appear to point out a more distant separation of ingredients, than is commonly or ever found in unaltered aqueous deposits. Mr Lyell thinks otherwise —
Indeed there appears an intimate connection between lines of metamorphic action & cleavage; changes in chemical composition from heat appear to occur in bands parallel to the cleavage. This would not occur, if laminated crystalline rocks were aqueous ones heated & metamorphied in no particular direction.
(a) Might not a laminated structure of metamorphic agency intersecting another & earlier system produced at period of aqueous deposition, account for those smooth & frequent planes of fissures, which are met with in some slightly metamorphised slates ???
Mem. the laminated structure in phonolites, where crystals of felspar are placed in a
given fixed direction
Laminated Lava. — Their alternating Layers of obsidian & feldspathic stone layers of glassey & stony pearlstone, in which cases changes in chemical constitution must cause their alternations. —
These facts prove a laminates structure to be produced by cyneous action
If all strata in time are liable to metamorphic action, how comes it, that so very large a proportion of metamorphic rocks have a cleavage, which is not the case with ordinary strata? This alone renders it probable that cleavage is affected during period of igneous agency. —
Many other such
case arguments can be adduced — V. Note Book1
1 The Santiago notebook.
If this opinion be granted; there is so much connection between metamorphic action & many lines of elevation, that all must be allowed to somehow connected. And that there is a connection (not without many exceptions) between lines of elevation & cleavage appears to be certain, from the general remark, that in stratification & cleavage the strike is parallel, but the inclination different. Now this could only happen, from upheaval acting in lines parallel to the laminae, for on any other supposition the strata would have a different direction for the cleavage.
This coincidence has been attributed to mechanical yielding in the direction of the laminae: although this supposition, by injection of masses of igneous rocks, would partly account for the parallelism of lines of metamorphic action & cleavage, & so only leave unaccounted for the original loxodromism in unaltered subaqueous deposits, yet I am inclined to seek some deeper & more intimately allied connection. I cannot believe the long chains, such as the littoral one of La Plata & Brazil can owe its position to so
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trifling a cause, as a slight familiarity in mechanical displacement. — Besides the cases of connection already pointed out, there appears in very many instances to
be exist to a close relation between lines of metallic veins, & the cleavage of the rocks, which contain them.
The cleavage from the nature of the formations, in which it is found either took place in deposits at the bottom of profound seas, or in stone rendered semifluid by heat, beneath great masses of incumbent strata.
We see, that it is a principle, which can act in the same direction after intervals of time; that at the Falklands it appears to have maintained a struggle against ordinary gravity; that it has the power, either during first aqueous deposition, or at subsequent periods of metamorphic action, or at both, to separate into layers various mineralogical substances. — The appearance of the laminated structure in the older rocks, has been compared to the oblique seams,
which such as are found found within true strata of sandstone: that there is a resemblance, in some points of view, is certain; but I must think, the cause in the
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two causes, to be very different. The action of currents, which, where best exemplified, show most frequent changes in direction, could never cause a loxodromism, extending over many hundred miles of country; & still less could
the it place the laminae in a vertical position.
In my notes on the geology of Chili,1 I have stated, that impalpable mud from the gold Trapiches, when thrown up into heaps, assumed a form concretionary-brecciated structure & that the speudo-fragments were divided by inclined even laminae. — What cause has affected this process? Chemical attraction, (of which, in the formation of may salts, there is abundant evidence) must have separated the ingredients: Have electrical currents, so intimately connected with attraction, determined the presence of laminae? May we extend some such view.? (a) Do currents of electricity flow, (as is supposed to happen in the atmosphere (?)) for long periods in certain directions, deep within the earth? Are they connected with the galvanic phenomena of
(a) It would be an experiment well worth trying to subject to a stream of galvanism. a fine mud composed of different ingredients, as clay, fine sand, pounded mica &c &c & to see what effect would be produced in the arrangement of the particles. —
metallic veins, as shown by Mr Fox?1
May we venture to imagine that these currents acting under certain circumstances, ؟ ؟ perhaps such as extreme depth, ؟ ؟ ؟ could metamorphise & completely separate the mineralogical ingredients of strata? That the subject is one of importance & no small intricacy will be granted by every one. Indeed the doubt & confusion between all authors, so curiously exhibited by Mr Greenough in his essay on stratification, (critical examination)2 is an argument that some power besides mechanical displacement, has caused the inclination of the laminated strata.
Conjectural, as the foregoing remarks & conclusions may be, they are drawn from a country, widely distant from frequent geological examination & in so far are worthy of some attention: After the study of S. America I cannot avoid the conviction that some great law of nature remains to be discovered by geologists. —
1 Fox 1838.
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