246A

Showing three sets of Plains

Thirsty Hill 43° not being in sight

[sketch]

A of sketch
C of sketch
D of sketch

Leading mark for East Channel

Woods Mount

in [type]

sketch in black ink on heavy white paper, by P. G. King, see DAR33.247 below.

Showing three sets of Plains] added pencil.

Thirsty Hill 43º not being in sight] added pencil.

Leading mark for East Channel] black ink.

A of Sketch, "C of Sketch, D of Sketch"] in ink.

Wood's Mount] black ink cancelled in pencil.

in [type]] brown ink.

246Av [blank]

245

1

1834. Jan. 10^th to 19^th. Port St. Julian

The geology of this neighbourhead all belongs to the great oyster formation. In the cliffs at the southern entrance point of the harbor the following beds are seen. — A green hard sandy clay, abounding with Ostreae, Pectens, Clams & Balanidae. — This weathers with difficulty & forms extensive flats above low water mark. — The above shells are excessively numerous & are as much cemented together by the fragments of balanidae as by the green earthy sandstone. —

Above this a yellower earthy sandstone, at this place characterized in an infinite number of Scutellae (b) &, as before, of Balanidae. — The Scutella are generally deposited into an horizontal position but sometimes groups may be seen on their edge, proving the action of currents. — 1792 ... 1799 With these shells are spiral Univalves, Pectens &c. — Box. containing shells &C. (1800) It may generally be noticed that the shells in different places occur in varying numbers. — at one place very many Anomiae, at other Turritellae, but the Balanidae (a) are universally numerous, as are the great oysters & Pectens in layers: Does not the presence of such numerous Balanidae indicate the neighbourhead of a coast in this ancient seas?

Above the Scutella bed is another ferruginous one of great oysters & Pectens. Above these beds there is a formation precisely similar to what is seen at Port Desire: viz tow beds the upper. white soft. very light argillaceous matter (a) 1729, the lower, not so white, with more unctious feel, & decomposing more readily into small angular fragments which form a talus to the upper bed. — On these rests the gravel of the Porphyries; but it is

245 verso

(a) Does this bed owe its origin to the decomposition of feldspathic rocks?

(b) The Santellae same as in New Bay? —

I omitted to mention. there are in this bed layers or lumps of concretionary calcareo sandstone almost forming a bed. 1730 1731 — also others of Limestone.

(c) I notice in the present day. deep sea soundings more constantly have fragments of Balanidae than any other shell. —

From 40 to 50 Fathoms of C. Virgins very generally fragments of Balanidae & some of a Spalangus.

The white beds contained Gypsum at this place. —

246

is about 90 feet high, of which the beds with organic remains forms about half. — Above the gravel, there is a bed of earth, this varies in thickness; in many places it has cut through the gravel & argillaceous beds down to the harder strata with oysters. (a) — It was deposited in water from horizontal arrangement of few pebbles, gained from the gravel bed. — It contains small stalactiform masses 1732 of Arg: Calc rock of a pale colour. (d) — In the place in cliff where the argillaceous beds are cut through there was a group of large bones; the whole skeleton probably had once been there. 1722 ... 1728 1736 ... 1745

The Vertebrae were in a line & joining on to the Pelvis; the small bones of the extremity were in group near articulation of main limit (1723). — This is interesting as showing the existence of large quadrupeds in Lat: 49°: 14'; in the southern hemisphere; the in its geological age being so clearly marked. — The earthy bed formed a tolerably level plain, on which were lying many Mytili (2 species) with their blue colour, Patellae &c & proving that it was at the bottom of the sea with great gravel plain. — Was this near the embouchure of some river in the old continent (or fisible elevated to land) when the large quadrupeds flourished? — It is the first time. I have

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246 verso

sea

(a) In parts of the earth there were masses, more argillaceous, & of a greenish colour & so hard as almost resemble stone. — These sorts of concretions & those of Arg; Calc: show chemical action

(b) It has since occurred to me, that perhaps this interstratification is only the re-deposition of earthy white substance, torn up by the gravel. — I believe in this explanation. March
It is hard the to reconcile the appearance of violence & chemical action in the deposit of the gravel. the crystalline nodules of gypsum & cut hardened beds like mortar, at the R. negro, must not be forgotten

(d) The Arg. Calc. rock is what I have called coarse Tosca rock, & the bed itself resembles pale impure Tosca excepting from the presence of masses of gravel. — Is it not nevertheless of nearly the same age?

the occurrence of the Tosca rock, stalactiform mass, appears to me very remarkable. — separated so many hundred miles from the nearest places northward, where with large bones they are to be found.

upper part of page excised

247

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1834. Jan. 10^th to 18^th. Port St. Julian

seen any matter superior to the gravel. —

Differently from what is described in the above cliffs, the white argillaceous beds generally are of great thickness; — they reach, with the exception of the gravel, to the summit of the highest land. —

Amongst the hills, & above such beds, there may occasionally be seen layers of oysters, with Turritellae & Pectens.

This proves no great diff: of age between oyster bed & white argillaceous matter in as much as they alternate. — On Thirsty Hill I found on the surface petrified wood 1720. 1721 (Mem: that at St Fe Bajada in sandstone in the oyster formation) & a Vertebra of some large, probably, cetaceous animal. 1719 — The Diameter was about 7 inches & stone very compact & heavy. — I have no doubt both these belonged to near where they were found. — At These cliffs, at entrance of inner harbor, 100 to 200 feet high, & composed of white Arg: matter (b) contained an abundance of transparent gypsum. — it occurred in vertical inclined, horizontal plates, one inch thick, which might be traced for great distances. —

The beds & gypsum same as at Port Desire. — (a)

On entering the harbor, a chain of hills appears to run across the head of it; in truth however the country is strewed with some flat-topped cones & small patches of table land. — Woods Mount is 956 (∠^r) feet high (c); standing on the little table of gravel on the top of it, it was an instructive lesson. to look round, & see only here & there at the distance of miles a truncated cone, the relics of a continuous plain. — V. drawing by M^r King¹

In a few more centuries these hills will be true cones, the few muscles

¹ Darwin refers to the drawing in DAR33.246A above.

247 verso

(a) I have omitted to mention, that in a specimen of the white Arg: rock, there is an impression of a shell (a Turritella?) 1733, it is the only sign of organic remains I have seen in these beds of Arg. matter. containing crystallized Gypsum:

(b) The Arg: bed here reaches down to the surface of the water. —

(c) Measurements made by Capt. Fitz Roy
False Peak 954 ft
Wood Mount 951 —
Thirsty Hill 430

The latter, as well as both former, was crowned by a patch of table land, & many of the near hills of same level. —

248

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1834. Jan. 10^th to 19^th. Port St. Julian

& limpets on the surface will be decomposed, & what will then remain to tell the story, that within a short period, these point formed the (level?) bottom of an ocean. — I imagine this. The plain could not have been as level as those of Port Desire &c.

Woods Mount is perhaps higher, than the other flat summits, & I saw one more distant hill appearing over a nearer. — Yet the country must have been table-land. —

In the vallies are several Salinas. which show a snow-white field of solid salt. (804 Tin label) They occur, as is invariably the case, in depression from which the valley leads. All the water is to more or less salt. —

The fact. that the white Arg: bed (b) lying on oyster bed & covered by Gravel in one plac should be so, in another hundreds of feet thick, is to me not very explicable. — I cannot believe its difference of original deposit; for a sea depositing such fine matter (a) would have more level bottom.

It only remains to suppose the gravel removed parts in the act of being deposited; but then we have alternations of Gravel & Arg: matter. — At Port Desire gravel immediately covered the oyster bed. —

G The gravel in this neighbourhead consist. (I should think one third) of a compact finegrained Porphyry. colour of fracture "wood brown" with tinge of yellow. [illeg], polished surface "wood brown & gallstone yellow" either without crystals, or with some quartz: also pale grey or greenish feldspathic with white crystals of felspar: compact green phonolite? some red porphyries with more crystals; some few, slate-looking basalt.

248

(a) The depression in bottom of old sea, where the entrance cliffs now stand, probably caused the deposit of boniferous earth to be formed there. —

(b) Perhaps more probably currents after a field of gravel was deposited, cut up the the bottom again the interstratification of gravel & white arg: matter might easily happen. — Perhaps these posterior currents might be connected with more than one elevation of the ground. —

March March After some reflection I have come to this conclusion: so many facts require repeated elevations & then we certainly should have as at Port Desire, the oyster bed & the Porphyry in places denuded & again recovered & as in this instance interstratified with the very substance the sea has been denuding.

I never-the-less think that the gravel & last regular bed were not long separated from each other. — Indeed, why should they? the sea never lies idle! —

curious similarity between attribute & system interstratified at P. Desire