RECORD: Darwin, C. R. Geological diary: Hobart Town. (2.1836) CUL-DAR38.837-857 Transcribed by Gordon Chancellor. (Darwin Online, http://darwin-online.org.uk/)

REVISION HISTORY: Transcribed by Gordon Chancellor and typed by Jan Nicholas; arranged against manuscript images by Kees Rookmaaker and John van Wyhe. This transcription is published in F1821.

NOTE: This document, part of the largest scientific document composed by Darwin during the voyage of the Beagle, is written mostly in ink. Marginal notes are here integrated into the text. Darwin was in Chile from February to June 1835. This period is treated in the Beagle Diary on pages 704 and following.

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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.


837

1836 February Hobart Town 837  (1 

In the neighbourhead of Hobart town, two distinct formations occur, each both accompanied by rocks of igneous origin. — R.N. p. 120 Granite on E. coast.
I will begin by the most modern of the two.

In this formation the prevalent rock is a white, finegrained Sandstone, composed of minute grains of Quartz, with a very little white cementing matter. Examine flints in 'Flo' formation for Infusoria. Within the town it is associated, with reddish laminated Aluminous Sandstones, other ferruginous ones & some Clay Shales. — On a hill close behind the town, there are strata of a very impure Coal, carbonaceous Shale, & white Sandstone, b&ed with the finest lines, stained black, by a similar substance. Here such layers are with all at a high angle & being disturbed penetrated by a great mass or dyke (a hundred yards wide) of a decomposing Greenstone; on one side the strata dip away at an angle of 60° or 70° & fragments of Porcelain rock & indurated sandstone, lying in the lines of junction, point out the con effect of the an igneous mass. —
Dr Scot's paper on Van Diemen's Land Annals of Philosophy. June 1834.
on the other side, the confusion is even greater; layers of impure Coal, being now in a nearly vertical position. —

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on a yellow substance in cavities in Trap. Daubuisson Vol II. p. 569

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1836 Febry Hobart town (2 

In the Government domain & in other places I saw the Sandstones & Greenstones abutting against each other with in straight lines.

In all parts of the hill, on which the town stands masses of Trappean rocks & al those of aqueous origin alternately appear; perhaps the & I am doubtful which class is most abundant. — The Stratification, in some places, as has been shown, is exceedingly disturbed & inclined strata generally are common; in many cases however, this is the result of the manner deposition, as has been described near Sydney, & hence the two classes are not easy to be distinguished.

Following the coast down to the South of the town frequent patches of this formation are met with. I found a coarse ferruginous Sandstone, containing tw numerous thin strata of Clay & highly ferruginous matter, reposing in strata layers, inclined apparently from original deposition, on a mass of coarse greenstone; the lower

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parts passed into the a Conglomerate, from containing so many pebbles of the underlying rock Greenstone & a white flinty rock, bearing peculiar Organic impressions & Sandstone, all which belong to the older formation & will be subsequently mentioned. —

Again further onwards, a coarse Sandstone containing some indurated clay is covered by some thicknesses of strata of a white soft alumino-sandstone, somewhat like the substance of Huepilacuy at Chiloe. — These are capped by a stratum of Basalt, a few feet thick, compact with scarcely even a minute vesicle & abounding with very small crystals of red Olivine 3(?) 3467. This is separated from a superior & exactly similar stratum of Basalt by one, which has an irregular outline, contains masses of hard Basalt, but is itself partly decomposed & resembles Wacke. — By tracing its graduations I found this com now comparatively compact substance once to have been Scoriae which without doubt divided two distinct streams 3469

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of subaqueous Lava. — The whole of this mass has been tilted at an angle of 30° to the South. — Following the Basaltic beach for a few hundred yards, there is a cliff, composed of a f very compact mass of highly vesicular stone mingled with some compact kinds. — parts have been broken & apparently reunited by heat, others clearly by the agency of water, as shown by containing two or three rounded pebbles.

The cells of the Vesicular Lava 3468, are generally linear, the lines being not infrequently parts of curves & the internal surfaces is are lined with sulphur (?). — I can feel no doubt, that this little point projecting cliff, although at present showing no trace of a Crater, was the point, from which the Basalt flowed. — yellow substance or stains

In close proximity we have the older greenstone, bearing almost the appearance of a Syenite 3445 & through this rock the former Volcano must have burst its way. — This is the only spot where I examined any Basalt; but in all the South part of both sides of the

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aestuary, the rock is found in platforms, which present to the sea cliffs, composed of magnificent columns. — In one spot I saw white horizontal strata, joining by a great vertical fault to such a mass & at no great distance apparently capped by an extensive stratum larger pile of the same substance. This was near Port Arthur, where a considerable mine of Coal (not of very good quality) is worked in Sandstone. —

I suppose of course these Carboniferous strata are of the same age, with those at Hobart Town & if so the great Basaltic Platforms & the 2 little streams of Lava, which I have described, belong likewise to one class of events. —

This whole formation occurs as a fringe, at the base of older series, around the aestuary; it likewise extends inland & partly comprises the lower grounds of the fertile valley of the Derwent. I do not think its elevation exceeds a few hundred ft. — We now come to the older

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1836  Hobart town (6 

formation of rocks, from the degradation of which the first series , have been formed. —

The upper strata, to the thickness of several hundred feet, consist of Sandstone; this rock is subject to some variation, but generally is of a yellowish or red color 3466,, hard, siliceous, & contains rounded grains of Quartz; I have seen some white & some quite red & not siliceous, but these are rather exceptions than common occurrences. — Close to Hobart town, there is such confusion in the strata, that I am very doubtful, whether some of the Quarrys, especially those at some height, are not worked in this rock. — Beneath this older Sandstone we have a very singular assemblage of rocks; they may be described as graduating in character between compact hard blue Clay-Slates, white Cherty or Flinty rocks, white aluminous fine Sandstones (or Claystones) & Limestones; each kind is occasionally met distinct & tolerably perfect; but the greater part has is of an intermediate nature.

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Perhaps the most abundant varieties might be named whitish flinty Slates. — These rocks abound with impressions of Organic remains.

the most abundant are those of the smaller stony Corals & of forms like Retepora; so I saw a few of these beautifully silicified: there are likewise the casts of numerous Terebratulae, & of one imperfect univalve. — At several three or four points, several miles distant from each other, a considerable thickness of the same Limestone strata have been exposed by Quarrys.

Beyond Newtown 3476 ... 3480 I found a compact crystalline, blackish brown stone, containing numerous some Terebratulae, & a few parts almost composed of a small Oyster; there were the impressions of a Pecten; the curious figures, representing Corallines, are chiefly found in the flinty beds. — The Limestone in parts becomes slaty & impure; it is very remarkable by containing an irregular stratum 3481, of unequal thickness of Snow white, soft (so as to be dug excavated with spade & pick) pure Calcareous substance; it is a

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1836  Hobart town (8 

soft chalk; it is not a little remarkable that such a substance should be included between strata of hard crystalline Limestone. —  

On the shore, a few miles South of Hobart town I found the following varieties blending into each other & alternating.

1st a white Cherty rock with grains of quartz 3457; a blue slightly calcareous, siliceous compact Clay-Slate 3458 & a greenish brown rather softer, coarser Clay-Slate 3459.

The whole abounds with impressions 3460 ... 3465; in it are scattered a very few rounded pebbles of pure Quartz, Quartz rock & some of a Micaceous Clay-Slate. —

The occurrence of a very few pebbles in the strata of this formation, is generally common. — Such happens in the Limestone & following cases. — On the flank of M. Wellington I noticed amongst similar kinds, 1st a pale blue coarse speckled clay Slate 3473 which perhaps would be called Greywacke), 2d white compact, uneven fracture aluminous stone 3474 & another similar one mottled blue & yellow 3475. On the opposite shore to Hobart 

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1836  Hobart town 9 

town, there are white strata & an excessively fine grained aluminous Sandstone (?) 3447 with an uneven fracture, which in parts becomes more sandy in other passes into a Porcelain rock with conchoidal  fracture 3448; the whole series graduates into an underlying blue stone partaking of the characters of Clay Slate. — In both are found rarely casts of Terebratulae & pebbles. (a) —

Near New Norfolk a similar white stone, passes into a very hard brittle sonorous siliceous one 3482, with straight fracture, whose grains of quartz. are blended & almost dissolved in a siliceous paste. Here pebbles of pure quartz were not so infrequent more frequent than elsewhere.

Mr Frankland the Surveyor-General, gave me specimens 3496 ... 99 of the white Aluminous stone, abounding with impressions of Shells. from the Huon River & likewise, a blackish Limestone almost composed of parts of Bivalves 3500 from the isd of Maria. (B) — We thus see this formation extends over the whole SE extremity of Van Diemen's land.—

With respect to its connection with the first formation

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(a) also all the strata are crossed by fissures the sides of which are penetrated with ferruginous matter, so as, from being harder, to project upwards. —

(B) I have also Terebratulae from the neck of the Peninsula (where the gards is kept) of the penal Settlement (3630: 31: 32). 

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1836 Hobart town 10 

I was not fortunate enough to find an actual junction; but as in this latter, pebbles from the 2nd & older series are found, the two formations must be quite distinct. In a like manner neither did I see the inferior junction; the white flinty Slates, were being the lowest stratified rocks which were are visible.

The pebbles however of Quartz rock & Micaceous Slate, show that a third & older formation must be not very far absent distant. — 

Yet in this immediate neighbourhead I believe the lower strata of the second series generally rest on a coarse greenstone which x  has burst through them. x when in a fluid state.

I think this, from the entire absence of pebbles of Greenstone in strata which are only a few feet distant from this rock; & from its close juxtaposition on either hand of masses of the stratified stones, which would appear to be the effect of violence. — I confess however, I saw no cases, where the Stratification pointed out this relation, in a satisfactory manner:

The strata are seldom horizontal, but are gently inclined, & as far as I can ascertain in 

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1836 Hobart town 11 

no particular directions. — Almost all the hills, even those of quite secondary height, consist of Greenstones. fringed with these strata. — On the opposite side of the water to Hobart town: a hill composed of ordinary, granular, & fine grained ferruginous Greenstones 3451 3453 3454, was skirted in the upper parts of its sides by gently inclined strata, which appeared (but I do not feel at all sure) to have undergone some alteration; there were bluish siliceous-Aluminous stones with minute grains of Quartz 3449 & white ones of a similar nature, which are indurated & fractured. 3450 —

Mount Wellington, the most conspicuous feature in this neighbourhead rising close behind the town, to the height of 3100 ft. is similarly constituted.— (Angular: M: Beagle)

Passing over the low ground at its foot composed of the first series, we first reach in the ascent the anomalous flinty & slaty rocks, then come to the Sandstones; these strata extend to a height perhaps of 1200 ft, above which there is nothing but Greenstone. — As the Strata on the sides are not very much disturbed. 

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1836 Hobart town 12 

perhaps this height nearly expresses the thickness of this formation. — All the Greenstone which crowns this mountain is of a very uniform character; it is rather coarse & contains crystals of Hornblende 3472 & yellow cryst?; it strongly affects the Magnetic needle; one side of the summit shows a large columnar structure; generally there is a grand accumulation of lo immense loose fragments. —

I have as yet only mentioned the Trappean rocks incidentally, some as belonging to the first & more modern, others to the second series of strata. From my limited observations I have not been able to ascertain any difference in these  Trappean rocks of two ages. — Indiscriminately over the country, we find ordinary Greenstone graduating into a granular kind which assumes a Syenitic appearance.  3451 3453 3454 3456

These probably belong to the older set, & are generally found in the higher hills; there are however numberless exceptions; on the coast some miles South of the town, there is a continued mass of a Greenstone 3455, composed of a irregular Feldspathic

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numerous Crystals of Feldspar & Hornblende (& Mica ?) imbedded mingled in patches of with a compact Feldspar feldspathic stone. This rock from a distance in mass, had the aspect of a Granite.

These Trappean formations (including in that name ancient Lava streams) prevail most extensively over the whole Island.— I hear everywhere of façades of Columns & detached conical hills. — The summit of M. Wellington is broard, level & of considerable extent; looking to the W. & NW numberless mountains of the same form & height, are seen; these in parts are said almost to form unite into an elevated central plateau.

I may here mention some facts obligingly communicated to me by Mr Frankland, which will give a general outline of the Geology of the Island .— The central mountains which occupy a large space; & of which M. Wellington may be considered as the termination in one direction, entirely consists of Greenstone. — On their Northern 

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1836 Hobart town 14 

boundary (20 to 30 miles SW of Launceston) there is an extensive formation of Limestone, Conglomerate, & Clay-Slate.—From Quamby's Bluff I have specimens of this latter rock marked with impressions of the Corallines & Terebratulae, so frequently mentioned. 2470 2471 — Hence there can be little doubt concerning the age of the clay. Slate; & when we consider the variable nature of the Flinty Slate & Limestone beds, containing pebbles, at near Hobart town; it is highly probable that the whole formation to the North belongs to the same one, of which the SE extremity is composed. We shall thus see one continuous series sweeping around the central nucleus of Greenstone. — On the NE coast, Granite is extensively found; & on the opposite extremity, the SW, there is a great formation of white Quartz; so conspicuous is this from its brilliant appearance, that Navigators noticing it from a distance, have thought it was to be Snow. — The level district at the sources of the Derwent & Tamar 

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1836 Hobart town (15 

are remarkable by the large quantities of silicified wood found there 3483 ... ... 3488; In the same district are found beds of Agate pebbles & these. Salt likewise is procured, from some ponds, which periodically in the dry season leave an incrustation of this substance. —

Perhaps these latter circumstances indicate another & distinct formation. —

Within the outskirts of Hobart town, there is a Quarry of Limestone, which I have delayed mentioning, because I am entirely ignorant in which class it ought to be arranged. The limestone is of a pale yellow color, not very compact, of a minute Crystalline structure; its strata are inclined at an angle of 45°.

It is everywhere traversed by very small linear cavities, which resemble those found in some Freshwater Limestones, to which stones this bears much resemblance. — Contains occasional layers & nodules of ordinary flint 3495 & still more rarely a few small pebbles. — Those which I saw were about twice as large as beans, & consisted of pure Quartz & Quartz rock. — In Some of 

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1836 Hobart town (16 

the lower strata, abound with distinct impressions of various leaves 3489 ... ... 3494, which are said to differ from those now existing. — Very rarely Shells have been found.in it. — The Limestone is covered by a mass of Alluvium, several feet thick, of rather a singular nature. Fragments of some Trappean rock, by their decomposition, now appear as balls imbedded in a Wacke; the interstices however & in parts, masses, consist of a quite white soft Calcareo-Aluminous powder. — This substance resembles a substance which was found under very similar circumstances at St Jago in Chili. —

This singular mixture of rubbish has also filled up a vertical fissure after the manner of a dyke in the Limestone, & until I found in it a rounded pebble, I was uncertain of its nature. — I suppose, the Limestone, after the displacement of its strata, but yet whilst beneath the Water, bearing lime in solution, was covered, by some subterranean violence with the fragments of Volcanic rocks. —

This kind of Limestone has only been found on the side of one small hill; as from the purity 

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1836 Hobart town 17 

examine for Bones

of the Lime, which is procured from it it is an object of value, it has been searched for with some care. — It is probable that this very limited formation was deposited either in a lake or small creek; the nature of the pebbles would lead me to class it with the older formation; but on the other hand its unconsolidated nature & the impressions of leaves connect it with the more modern series.

I now come to a subject which I have so frequently discussed in my Geological Memoranda; viz recent movements in the level of the land. On both sides of the Bay & along nearly the whole line of coast, sm quantities of broken shells are found on the land to the height of 30 to 40 ft in quantities which make it rather difficult to believe they have all been carried there by the Aborigines. Amongst these shells are found many rounded pebbles & individuals two small to be brought for purposes of eating; the coast moreover in a few places, by its outline, obscurely shows a small 

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 vertical retreat; on the other hand, much of the shells appear collected in heaps, in which nature instruments of the Natives have been found & hence clearly bespeak their origin. — In Ralph Bay, Mr Frankland, who accompanied me in these excursions, & myself, found a beach from 12-15 ft above present high water mark, many of wh & covered with vegetation, the many of the pebbles in which, were coated with Serpulae. This instance is of no value, because the bay. creek is only separated from a larger expanse of water, by a low strip of land, which the tides might have heaped up, & before this had happened, a higher surf might have thrown up the beach. (a) —

Again on the banks of the Derwent River, where the water is fresh or so brackish that marine shells will not live even for some miles lower down, the same layers of shells, intermingled with masses of shingle are found on the banks, elevated from 6-10 ft above the present highest tides (b) (b). Now before When the bay was less filled with the 

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(a) N.B.: That changes are still in progress in this little cove is certain from the fact, that oysters which two years previously were abundant, have entirely ceased to exist.

(b) I may mention also that some of the little side valleys have that peculiar flat-bottomed structure which indicate that they formerly were occupied by the water as small coves

[Page 19 in this sequence is absent.]

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Australian caves. — Mr Frankland has determined to investigate this subject & likewise the recent rise of the land; there can be little doubt he will make some interesting discoveries.

Before concluding I will give a summary of the history of the formations; but when it is considered that this Island nearly equals Ireland in extent, it will not be manifest what a shadowy outline such must be.

At a very early period the great Quartz formation in the SW part of the Island extremity probably existed as one or or more island; as likewise perhaps did the Granite of the NE. — In the surrounding or intervening ocean, thick mass of strata were accumulated, which compose the second series; Hence we have the pebbles of pure quartz & Quartz rock.— 

In this sea Corallines abounded, & amongst them numerous Terebratulae & beds of oysters. — During this epoch, the subterranean forces propelled upwards large masses of Greenstones; this propulsion appears to have taken place 

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(a)  for some other rocks v. Lesson's Zoologie

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in mass, & as the superincumbent strata are not much displaced, without any much partial violence. — In this state we either have an Archipelago crowded with Islands or a land deeply indented by arms of the Sea; in such spaces our first or most modern formation was deposited from the wear & tear of the older (a) (a). — During this period also igneous rocks were both poured out as Lava streams & by injected masses violently ruptured the strata.

We believe lastly the land attained its present position after some considerable oscillations of level. — 

In attempting to compare the Geology of this country with that of the Colony. of New South Wales, a considerable resemblance in each place may be observed in the Carboniferous series, which in both places forms the upper series formation.

At the distance of 600 (Geograph:) miles it appears very doubtful how much confidence may be given to such resemblances in ascertaining their respective coeval origin. I think 

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(a) I should observe in such newer patches of strata, many probably belong to considerably remote rather distant periods of time but in this first rough classification they come into the formation. —

'Macc. Class of Rocks p. 471 on Hypersthene rock appearing at passage from greenstone to syenite.  

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however it is not improbable, that on an extended examination, a considerable degree of parallelism in the formations of the two countries would be discovered. The Limestones of Argyle with Organic remains, might correspond with the second series of this place, & the Quartziferous Granites of Australia, with the Quartz rock of Van Diemen's land. —

With On first two examining the country, from the preponderance of Trappean & ancient Volcanic rock, I was struck with the resemblance of it to New Zealand. — There also I believed there were two distinct formations; the older containing Limestones & Cherty beds, & the more modern Lignites & Sandstones. — 

With respect to the absolute age of the second series of this place, I fear the fossils are far too scanty even to offer a conjecture. The re subject remains a field open to the examination of the rising Geologists of Tasmania. —

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May 25, 1836, Memoir of Van Diemen's Land, of Mr Frankland1 

1 Frankland 1836.


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