RECORD: Darwin, C. R. 7.1836. Geological diary: Ascension. CUL-DAR38.936-953. Transcribed by Guido Chiesura, edited by John van Wyhe (Darwin Online,

REVISION HISTORY: Transcribed from the Darwin Online images by Guido Chiesura, corrected and edited against the manuscript by Kees Rookmaaker, corrections by John van Wyhe and Gordon Chancellor 8-9.2009. 953v was transcribed by Gordon Chancellor, corrections by Rookmaaker and van Wyhe. Corrections and textual and editorial notes updated by van Wyhe 8-9.2010. RN6

NOTE: This document, part of the largest scientific document composed by Darwin during the voyage of the Beagle, 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.

The pages are numbered consecutively 1-35 in the upper right (recto) or upper left (verso) corner in ink, probably contemporary with the writing of the notes. The paper size is uniform, 20 x 36 cm (8 x 10.3 inches).

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.




During our short visit of three days I chiefly confined my attention to some singular facts  respecting the mineralogical nature of some of the certain rocks, & thus was not able to understand but very little of the general structure of the Isld. —

There [are] most important references in D'Aubuisson on scoriae in Thonolite on siliceous infiltrations & veins and on lamination of trachytic rocks

Its form is that of a slight irregular triangle, each side being about 6 marine miles long. The whole is of a volcanic nature; & from the absence of any proof to the contrary, probably is I suppose of subaerial origin. — The basal & inferior rocks all consist are of a pale colour, compact, & of a felspathic nature. In the SE part, where the highest land occurs, trachyte & other congenerous kinds of that varying family compose most of the hills. — The lower parts thorough the Isld. are concealed  by black most rugged streams of basaltic lava & here & there an intersecting spur valley smoothed over with alternating layers of ashes. Volcanic sandstone cinders & Pumice. Yet the basaltic
It appears from Bory St. Vincent [one word deleted] accounts that  he observed some such structure in bombs of Mauritius says cellular inside and porous externally



rocks. in places have remained uncovered. — At the foot of Cross Hill, a considerable quantity of pearly white & brown Trachyte with a granular base containing atom-like black crystals & others, of broken & contorted glassy felspar is from partly overlapped by a black highly vesicular basaltic lava (with olivine & cryst. of glassy Feld). — 3736 3741

In the centre of the Isld. some hillocks of brown. & dark grey, heavy, (vesicular with minute irregular linear cavities) felspathic lavas are similarly situated. — 3737 3738

To the North of Long Beach, in a ravine, a mere point, a few yards in circumference, of a grey compact homogenious. slightly cryst. Feldspathic rock 3772 (with obscure laminated structure) alone tells over what the the superficial streams have flowed. — With respect to the modern lavas, though some are highly vesicular, others are but little so: 3771 3765 — in parts they assume singular forms, of which regularly flinted kinds are exceedingly regular common. — Specimen (3770) closely resembles a piece of wood. without the bark. — They generally appear to have possessed, when in a melted state, but a low degree of fluidity; the edges of the
41 [some] crystals of plan.



streams are very thick, forming steep cliffs, frequently above thirty feet high. — The surface moreover is extraordinarily rugged, over it are interspersed irregular conical hillocks, which viewed from a short distance resemble the drawing of the spiracles on the famous plain of Jorullo. — The greater number at least if not all certainly have no connection with never in any way been points of eruption; their height varies from 10 to 30 ft, their bases are rather broard; they are composed, like the more level parts of the stream, of a fractured mass of scoriaceous & more compact basalts. In some cases, an obscure vertical structure, traverses the central & most compact part; in other cases, & likewise on the more level parts of the lava, ribs diverge outwards. — These ribs consist of a convex surface, built of angulo-globular balls of lava & resemble the crown of arched gutters, but they do not appear to be hollow. — The origin of these cones or hillocks, must, I suppose, be owing. to some



inequality in the consolidation of the lava, causing it to be heaped up in these such points. — The most rugged (& in truth it was wonderfully so) stream which I saw, was composed of a black basaltic base, smally vescicular (3739) (& amygi? with glassy felspar?); its margin, where abutting on a level plain was steep & high. — It is one of the most modern in the Isd.

Note This stream occurs in the SW extremity of the Isld; its rugged surface is whitened by the dung of the sea fowl, which perhaps frequent it, from its extremely rugged outline. — In several parts in cavities of the lava, large irregular masses of a compact, yellowish brown  substance divided into thin slightly curvilinear layers, may be met with. 3746: 47; 48

When broken, it is seen to be traversed by thin layers of some saline matter, & it emits a pungent & rather nauseous smell. — I imagine this to some form the substance owes its origin to an infiltration of the birds dung. — Does it resemble the Guano of the coast of Pem?. The neighbouring rocks are in many parts, thickly encrusted with arborescent & stalactiform masses of a firm harsh white earthy matter, which does not effervesce with acids.(3749) [pencil] refer to Journal St. Pauls. —




The imperfect forms of these incrustations, seem to show a contraction, & partial removal of some substance. — Do they owe their origin to the indissoluble parts of the birds dungs, washed clean by the rain & then hardened? What is their composition? Do they resemble the arborescent masses out on the rocks of the Abrolhos? —

Chronology of degradation. perhaps

From the arid nature of the climate, it is probable that, with the exception of the surface growing, a little dull, the lava would long remain. in its original. state. — Such has been the case for within historical periods now extending through some centuries, no eruptions are on records, — nor at present are earthquakes or any indications of a yet active volcanic power ever experienced . — (a)

The sources, whence the modern basaltic lavas have flowed, may be traced north to the isolated red conical hills, which chiefly rise out of northern & western parts sides of the Isd; and likewise to the basal parts of the great. Trachytic mass of hills the centre.

(a) On the other hand geologically speaking the Isld. is extremely modern. — In no part has the sea worn the rocks into steep cliffs. — & from the absence of all such natural & deep sections of any depth I did not see even one single stony dike. —

NB I see there are cliffs on one limited part on East coast.

The SE end is the [Trachytic] & ancient end these lavas late cliffs???

Chronology of degradation. perhaps] added pencil.

NB I see there are cliffs on one limited part on East coast.] added pencil.

The SE end is the [Trachytic] & ancient end these lavas late cliffs???] added pencil.



V Lesson From the summit of the Green Mountain, looking round the Isld. between 20 & 30 hills of various sizes may be counted in which a truncated or slightly hollowed top indicate the former existence of a crater. — P 70 Scrope on same subject W Indies. In several of the truncated hills, in several the slope summit has a slope directed to the SE or to windward. —

R.N. p. 3 quotation from Scrope

Is a fact noticed by M. Lesson in the Zoologie de la Coquille — I suppose it must be owing to an original inequality owing to caused by the action of the trade wind on the ashes of lighter ejected matter. —

Mr. Hennah Geolog. Proceedings 1835, p. 189 beds of ashes at Ascension always occur on the leeward side of the island. —

Some of the craters have cast forth the bodies called Volcanic bombs; in the vicinity of one, which probably was the source of the extremely rugged lava stream in the SW. extremity of the Isd. many of these rounded shapes were lie strewed on the ground. they vary in size from twice the size of a man's foot to that of his chest; their forms are spherical, or elongated, or the lower half is rounded & the upper with irregularly points. — The surfaces are not glazed but they are commonly fissured by branching cracks [small sketch]; excepting fom the figure & an occasional concentric structure, they could not be distinguished [continued on p. 939 lower left margin]

They consist either of scoriaceous & more



[text in lower left margin, continued from p. 938v] from any rounded mass of cellular lava.

Bory St Vincent

compact blackish lavas, mingled without order; or, more rarely of a central very cellular mass. surrounded by a concentric case of more compact kind, which again becomes scoriaceous to form the superficies. (3740) — I observed this fo structure too often, for it to be an accidental occurrence; although its explanation is not obvious. — All the bombs, even the larger ones, could be easily broken. by one or two heavy blows of my hammer: yet yet many were lying on a surface of solid rock; — how did it happen that they were not dashed into the smallest atoms from the shock of their great aerial fall?  Must we not believe that a thick & soft bed of ashes spread over the country, but which long since, from the action of the winds has been partially removed, preserved them from any, too violent a blow.? —

We will now turn to the structure of the great trachytic mass, occupying the SE division & part of the central division of the Isd. — The high land, included within a line passing round the bases of Holyhead, Weather Port Signal, harden Mountain house

[calculation] 752 [divided by] 6 [no outcome]



& the old crater, called the Riding School, is thus mainly constituted. — The most abundant variety is a white soft stone, appearing like a tufo, which, together with some obsidian, & other laminated felspathic rocks, will be particularly described. —

Common white & grey, well characterized Trachyte 3773 3786 with black cryst. specks & [broken] cyst: of glassy felspar, is common. — I saw numerous fragments of Hornstone Porphyry; others of brecciated tufa, of the position & nature, of which & likewise probably of many other kinds, I am from my too short examination, & am quite ignorant. — There was one block of conglomerate of so singular an appearance, as to be worthy of being mentioned. — Small rounded pebbles of subst granitic, jaspery & volcanic stones, 3774:75 are embedded in a ferruginous base, but the whole is mixed with patches & thin layers of pitchstone, passing into the nature of Obsidian. A mass of small ejected fragments must have been penetrated by the latter substance & possibly even might have flowed as a lava. —

These hills of white & decomposing stones, have been fractured with much violence : many small faults are clearly perceptible, others




on a much grander scale are less obvious. — The great stratified mass appeared to have been tilted into a nearly vertical position: fissures transverse the rocks, some of which are filled up with decomposing Volcanic fragments, others remain open, & appear to be of great depth. — These latter must have originated posteriorly to all marked changes in the nature of the surface of the Isld. From I was unable (perhaps from limited time), with the exception of the riding school, to trace in any of the hills  * a crateriform structure, & I do  not know, whether they form parts of one great, or of the several orifices. — Within the limits of the bounding line, which was above assigned, some basaltic hills arise. Geograph Journal Green Mountains, 2800 ft high & the most elevated point in the Isld. isconstituted situated in the midst of the trachytic formations: — The only lava stream, belonging to it, which I examined, is black basaltic & highly vescicular 3735, it is covered by a great accumulation of black scoriae. — The summit of the mountain is compose formed of a ridge &

Geograph Journal] added pencil.



peak, composed of a pale coloured decomposed brecciated mass of small volcanic fragments. — Around the greater part of its base, an highly inclined quaqua versal dip1 is manifest.

The strata are composed of ejected fragmentary matter, agglutinated together. — In a like manner the surrounding country is levelled by a mass some hundred feet thick of similar but horizontal strata. —

The lower part Of these the inferior part consists of even regular & thin laminae of a fine grained, dark or pale brown, volcanic sandstone, which is sufficiently compact firm, so as not to crumble beneath the fingers. — 3734 Above this comes a coarsely divided mass of large angular fragments, many of which are of Greystone lava. — This again is capped by finer beds owing their origin, as in the first case, to ag agglutinated ashes. Some of the layers, contained considerable quantities of pumice, which where decomposed, & formed a white soft, brecciated, but nearly homogenious, mass. — One of them, was singular, from the palpable manner,

1 quaquaversal: Dipping, pointing, or occurring in every direction. (OED) KR



[sketch in margin]

with which it showed the setting down of the overlying heavy fragments. Beneath each of these, the white ribbon was bent into deep, but unbroken curves. — From the nature of these accumulations & the form of the Green Mountain, it probably, in its last state of activity, existed as a volcano, with a narrow mouth, which, like a great air-gun, projected large much loose matter & no lava. — In the neighbourhead, considerable numbers of fragments of rocks, which do not appear volcanic, are found mingled with black scoriae. Mr Evans presented me with some specimens, —  One has the aspect of a Syenite, the felspar is in elongated semiopake crystals 3742: the part, which I imagine represents the quartz, differs however but little, excepting in its more granular structure; the mica, or hornblende has a fused appearance. — A second appears like Labrador felspar 3743. Two others, which are described as coming from a red soil 3744 3745, have a truer granitic character; the quartz is reddish




& the mica either altered, or converted into black augitic like crystals. —

Towards the Eastern end of the Isld between Green Mountain & Weather Port Signal station, there is a remarkable oval depression, which is well represented in the plan of by Lieut. Campbell R.N. — Its greater axis is about 3/5 of a mile long; the bottom is smooth & perfectly horizontal (Hence called the Cricket ground): the walls are nearly 400 ft high & so precipitous as to be inaccessible excepting by at a few gullies points. — The lower half of these cliffs consists of a compact Greystone & Basalt, containing good sized cryst. of glassy felspar 3732:33: it has an obscure columnar structure; some parts of these rocks pass into cellular varieties & or such for obscurily & are then irregularly stratified; but these lines of division are neither horizontal, nor do they incline in any determinate position. — The upper half is made up  of the thin horizontal layers of sandstone & ejected fragments which have been above described . — There, on opposite parts of the margin & on opposite sides, although they appear truncated, as if having once formed one continuous mass, in parts have been deposited posteriorly to the existence of the hollow. In

Conglomerate] added pencil.




[sketch in margin]

two or three places, where the cliffs are not steep, these horizontal strata slope inward & less grow thinner; which latter circumstance must be the natural consequence of the greater extent of surface in proportion to the falling matter, & likewise to a greater facility in its degradation. — From this fact, we must conclude, that the flat bottom of the Cricket ground has a thickness of such strata, at least equal to that of the surrounding country. — & probably much greater, from the matter brought down by alluvial action. —

Less difficulty in accumulation & probability of removal after frost falling

This most remarkable basin, which at distance somewhat resembles a crater, is terminated at one end, in the line of its longer axis, by a narrow short gorge & at the other, by a partial depression in the surrounding margin. —

most interesting feature in geology analog with Galápagos 

direction (?)

I conceive its origin. must be attributed to a nearly circular mass on a line of fissure having subsided, — a case perhaps analogous to those instances, in which a volcano after eruption has suddenly been converted into a deep lake; which last circumstance with under a less arid climate would here in this same time here likewise occurred. —   

I have as yet only alluded to the white soft stone, which forms the chief

Less difficulty...frost falling] added pencil.

direction (?)] added pencil.

on a line of fissure] added pencil.



part of the trachytic mountains. I first examined it at Weather Port Signal Station; it is there has a quite white, dense, yet friable under fingers feldspathic earthy base, embedding cryst. of glassy feldspat. & microscopical black specks; it contains also small irregular fragments of dark scoriae 3783, the cells of which are sometimes partly filled with the white substance. — Hence the appearance is that of a tufo tuff; yet when examined under a microscope has the it would be better thought a crystalline rock. — This stone is traversed by curvilinear plates of a rock, which I think any every one would call trachyte; — a pearly base, with the usual crystals & some spots of ferruginous a purplish colour 3784; they will be shortly will presently be presently described with more minuteness. — In a second locality, at the northern part of Green Mountain, the same soft stone is associated with a homogenious, pale grey & white laminated Felspathic stone 3785, containing a few crystals & some minute & irregular vesiclescavities. — It will hereafter be  shown that laminated rocks of a  glossy identical nature alternate with & pass into layers of obsidian
These two associated rocks are traversed by the same hard plates, & are both intimately connected with a huge pile of solid trachyte 3786 (with numerous small black crystalline points & glassy felspar &



& brown patches). I was unable to to discover the exact nature of the junction. —

(a) Note. I was guided to this & some others localities by Lieut. Evans of the Royal Marines; to whose kindness I am much greatly indebted for much curious information. —

(a) Thirdly, at the low rounded Hill, with a crater-formed summit, called the Riding School, the general aspect of the formation is precisely similar to that of the Weather Station.

(b) In no part of the Hill could I discover any stratification. —

(b) The stone is of two varieties; the one 3787 smoke grey, friable, with few cryst. of glassy feldspar, black specks, & small angular brown patches, in all which respect it is obviously the same with the hard trachytes; the other is of a darker, green grey, is much harder & more of a contains more crystals of feldspar & has a more evident general crystalline structure 3788. These two are associated together in a singular manner, at one times they pass into each other & at another, the dark grey one recurs in quantity embedded in the semi-rounded fragments amongst the white. — Both kinds occasionally contain small fragments of scoriae, a few partly rounded pebbles, & several grand angular blocks, some tonnes in weight of a purplish black Porphyry. 3796: 97: :98. (with numerous fractured semi-decomposed crystals of feldspar & others ferruginous & vesicular cavities crossed with hairs of brown analcime) — In both kinds masses of veins of a coarsely honeycombed




ferruginious stone, which at first sight strongly resembles some, non uncommon, varieties of sandstone. 3789 — These masses are frequently attached to the plates, which most abundantly occur side traverse every part of this hill as in the other localities. These plates or veins consist of a very hard brittle rock, either grey or brown; the base is partly homogenious, partly crystalline; it fuses with some difficulty! into white enamel under blowpipe.  

it contains some few crystals of glassy felspar, & numerous black cryst. points sometimes aggregated in patches; Hence, excepting in the nature of the base, it is precisely similar with the surrounding soft stone. 3790 to 3795 — It has not so much the aspect of trachyte, as that of the Weather Station. — These plates vary in thickness from one tenth to an inch in thickness. in parts they thin out to nothing leaving irregular holes apertures in the plates. — They lie in all planes, from vertical to horizontal, & interbranch one with another; commonly they affect curvilinear forms, so as to include masses of many yards square of the white stone. — They long resist decomposition; hence masses of the soft stone most singular figure protected by these natural shields, stand out. — I saw one where a pedestal of the white stone was capped by a hemispherical plate, like an umbrella, & capable of sheltering

Mem quantities of siliceous veins in upper part of this hill.

Mem...this hill.] added pencil.




more then one person. Sometimes the veins although so thin project upwards although two or three feet & extend in length for a few yards. They are, in such cases, both to extremely sonorous, emitting, when struck, a sound like a big drum; & likewise elastic, this last rare phenomenon not however being perceptible in hard specimens. The whole surface of the hill is thickly strewed with fragments, hence in walking over them, a noise is produced as from the basaltic clinkers in the Galapagos Isds. — I have never in any other country seen veins of similar forms; if I was obliged to compare them with others, I should say they most resembled the thin ferruginous plates which traverse occur in some sandstones. —

In reviewing all the above facts, in order to come to a determination, whether the soft white stone, with its veins, is of aqueous deposition, or of igneous origin, a more contradictory mass of evidence is produced, than in my small experience, I have ever before met with. — The general aspect of the soft stone which is like a tufo; - the embedded fragments of scoriae, especially the small cellular pieces; — the laminated structure in the parts, where such occurs; — the breccia — conglomerate formed by the dark greenish grey & white stones; — &



lastly the forms of the plates, which are totally unlike those of dikes; — all seem to declare on the side of Neptune. On the other hand, — the structure of even the softest kinds, which under the microscope, certainly appear which is clearly crystalline: — the exact agreement, in crystals of glassy felspar, microscopical black specks & dark coloured small patches, with the hard trachytes; — their connection with that rock; — & lastly the intimate association, or rather the identity of the laminated kinds (as will be seen) with obsidian; are too many facts grounds, which appear to me scarcely controvertible for the an igneous theory. — exact point in case Daubeny p. 180 We may imagine that extraneous fragments could easily be involved in a lava stream; & under like manner similar circumstances we known, that a brecciated form structure occurs. Mem. Dauberry same case. As for the laminated structure I must again refer to the obsidian in which formation it occurs is present in a much more perfect degree. — In conclusion, I incline to the belief that those soft stones which now so much resemble tufos, flowed as trachytic lavas; & that they have since undergone partial decomposition. With respect to the plates it is possible, that water holding (or vapour) siliceous & ferruginous matter in solution, might have followed fissures caused by contraction &

Mem. Dauberry same case.] added pencil.

(or vapour)] added pencil.



have rehardened the soft altered stone. I was led to this conjecture, which perhaps may account for the figure of the veins, from observing in the higher parts of the same hill, tortuous veins of agate, which have affected the surrounding stone, to some distance.
describe section in detail

We now come to the obsidian, which has been so repeatedly referred to: it is found at the base of part of the white hills belonging to the trachytic series. —

Daubeny on alternations of glassy & stony [hot] lavas. p. 95. —

The lowest bed, judging from the fragments on the surface, must be several yards thick; it is covered by softer laminated stone in which at intervals the obsidian twice appears in irregular strata. — dip inwards. The formation on the East side, is covered up by a large modern basaltic stream & on the west passes under an accumulation of pumice & ashes. — The obsidian is of an intense jet black & with a fracture which is a model of a bivalve shell, it sometimes yet scarcely passes into Pumice 3801: It is covered by a grey hard, carious feldspathic rock with thin slightly convoluted laminae, which closely resemble in some parts a flinty slate, in others silicified wood. 3804 —
that these tried several people

The obsidian  either abruptly appears in this rock in large nodular masses, or more commonly in thin alternating layers. — These latter rocks

describe section in detail ] added pencil.

Daubeny on alternations of glassy & stony [hot] lavas. p. 95. —] added pencil.

dip inwards.] added pencil.

that these tried several people] added pencil.



are singular; the thin layers of Obsidian, which in these cases always appears of  a greyish green colour, either have the form of veins 3802, or of small angulo-nodular balls, varying in size from a large shot to a bean, which and embedded in a [spring] white pumiceous powder. — They were associated in one case with small ferruginous nodules. 3803 :05 06: 07: 08. The layers of hard grey felspathic rocks, frequently have a character approaching to obsidian itself; sometimes they assume a white pearly nature & small nodular structure, in which cases they easily pass into obsidian; & again the layers of such nodules pass into the compact, dark coloured obsidian. — These laminae, like all the others in the series are highly inclined, & slightly twisted: in some specimens they are so thin, are that they may be compared to the finest ribboned felspar agate . — slight alternations of colour may be observed of a thickness varying between one or two hundredth & one two hundredth of an inch: — The flinty looking felspathic slate [whi ours] is associated with some pale reddish brown hard homogenious felspathic rocks 3811; also with others of a blueish grey stony nature, which alternate with layers of a harder whiter kind 3809, these latter forming

[whi ours]] added pencil.




convolutions around small carious hollows.

such fine laminae

The weathered surface wonderful

Moreover we have another rock intimately associated with the above; it is hard &compact & is composed of excessively fine alternations. of a blueish grey & pale brown crystalline felspathic stone, containing a few cryst. of glassy felspar & numerous minute linear-shaped black (iron ?) particles 3810 3814 loose fragment. Phonolite? Trachyte? is ours

In the neighbourhead there were so many loose fragments of a rock somewhat allied to this last, that I cannot doubt it belongs to the same series; it is quite compact, hard, heavy, & at first sight resembled some primitive greenstone; 3813 Hornblende??? it has a granular structure, of two distinct minerals, but the felspar is of too glassy a nature from the rock to which I have compared it. — All the foregoing varieties are associated with, & pass into, a compact, blueish grey felspathic stone 3812, possessing an obscure cryst. structure, an uneven fracture & some  minute vescicular cavities. This rock again goes upward assumes a few white slightly tortuous lines 3815, becomes rather softer, with a more earthy fracture. — These become as thinly laminated by white planes which are barely perceptible 3816; — is allied to the rock resembling 3810, but wants the black particles, & likewise to the laminated rock (3785), so frequently mentioned.

such fine laminae...surface wonderful] added pencil.

Phonolite? Trachyte? is ours] added pencil.

goes upward] added pencil.

Hornblende???] added pencil.



as connected with the common tufo-like stone. — These latter varieties form soft decomposing white masses of considerable thickness, between & over the beds of obsidian. — The white series Having traced so minute a gradation in character from these softer beds to the black obsidian, & some of the intermediate forms. appearing, such as the moresmally vescicular blueish grey stone (3812), & the crystalline laminated varieties, appearing like igneous rocks, I feel no doubt in attributing the white to one series of lavas which cannot geologically be separated. [text inserted, see next page] — The laminae of the whole formation dip towards the mountain, of which they form the base, but as I do not understand the structure of this district, I do not know what relation these plains of division bear to the of original position of the whole mass. The excessively fine layers laminas changes in composition of these rocks not in all cases graduating into obsidian, are curious. ( ¿ does not such fact happen in Peru ?); it is clearly analogous to the fissile structure of some ordinary lavas, & phonolites. — In conclusion, I may remark, that on laying

R. margin       

It would be most difficult to persuade [look] subaqueous nodules like agate

I cannot doubt if obsidian were not known [begin at due] as I would suppose. — [on next page] 2 - kinds of obsidian like 2 basalts

Nodular structure clearly like that in aqueous deposit [on next page] obsidian different chemical preparation to Felspar

Glassy somtime effect of cooking walls of dark surface of [cular] lavas experiment

Origin [illeg] structure, [illeg] fluidity

It would be most difficult...structure, [illeg] fluidity] added pencil.



by the side of each other pieces of the black obsidian, the white fibrous pumice, the flinty like slate, the homogeneous blueish grey stone, the earthy & crystalline thinly laminated rocks, it was with astonishment that I came to the conclusion, that all formed part of one series (whatever might be causes of variation) which could not be separated; & that they were all equally the products of volcanic heat. —

I will now return to the hill called the Riding School, which I have described as chiefly constituted of the white stone, with the plate like veins. It is of a rounded form, & is surmounted by a circular, sauce—shaped summit, of about half a mile in diameter. The hollow has been nearly filled up with alternating layers of loose ejected fragments, which all dip to the centre with perfect regularity. From this cause reason, & the appearances are strong, this depression has generally been supposed to be an ancient crater. In the greater part, however, of the external circumference, no crateriform dip dip, or stratification of any kind is distinguishable, which alone would

[Notes from the right margin of page 22]

These facts show that mere pate or manner of cooking is not the only determining cause for the production of Obsidian or glassy lavas.

Layers of obsidian analogous to layers of Hornblende points

Properly Devil's Riding School is same with "Crater" on Lieut. Campbell Plan

These facts show...Campbell Plan] added pencil.



render the origin doubtful. Moreover, part of the margin is formed by irregular hills of lava; one of them on the northern side consisting of compact & cellular grey basalt. — In one place, the dark grey trachytic rock (3788) is traversed by a broad, vertical, irregular tortuous vein, which appears like a compact red sandstone; it contains more then one seam of a pinkish or white stone substance 3776: 77: 78 intermediate in character between agata & Jasper: it is very hard. — The so called sandstone, I believe to be the soft trachyte rock, altered by infiltration. Is it fusible — A little further on, considerable masses, but I do not know whether in veins, of a pale yellowish jasper, with small irregular cavities, containing a ochry aluminous powder, are found. 3779 — Again in parts, the whole surrounding rock appears to have a tendency to pass into red jasper. — Beyond this, we come to the mass of volcanic rock, mentioned as forming part of a margin; here a slaty compact lava, is associated with a brecciated, finely scoriaceous mass, which latter is thickly coated with white & red, mamillated siliceous coating. (Hyalite ?) 3780




Parts of the same mass contained angular patches of true red jasper 3782 poor specimen: it was, at the time, the impression on my mind, that the presence of the jasper was someway owing to the siliceous & ferruginous infiltrations. Moreover Besides the [red], in the close neighbourhead, within the same lava, there are extensive masses of regular ochre & yellow jasper. 3782

Like saucer within saucers of different colours

Within The saucer-shaped summit, the marginal & inferior strata dip towards the centre at an angle between 20° & 30° is composed of ring within ring of the bassalt edges of successive strata: the marginal ones around whole circumference dip towards the centre at an angle between 20°& 30° & so pass beneath the others; the next ring dips in same direction, but with a decreasing inclination; & so on, untill the centre consists of remains a circular nearly & horizontal disc. This structure necessarily results from a horizontal section, (produced by superficial degradation acting especially near the margins) which has cut through the successive accumulations of matter in a saucer-shaped hollow. — The outer ring or band is composed of layers of white friable pumice & from this color & its circular form of equal width, when viewed from a distance, it appears like a place, round which horses have been exercised, & hence the

Like saucer within saucers of different colours] added pencil. 



name of the Hill. — Within this, succeeds a brown band of small decomposed scoriae; again white pumice; a thick mass of yellowish & pink, very fine, decomposed, but slightly compacted ashes; again white — pumice, capped by the central disk about 8 ft thick of small minute fragments of black glassy seam cinders. — which is about 8 feet thick. —  ++ Pone infra. The surface of the hollow is even, but slopes a little to the southward. — ++  I have only mentioned the principal changes; besides these, there are many trifling ones, each of which forms its own ring; from this cause & the perfect regularity of dip, the appearance is, if I may use such an expression, quite comical. — (++. —) The substances, of which these strata are composed, from the small quantity of each kind, probably preceded from a Volcano somewhat distant (note +++); they do not appear to have been accumulated under water, but the successively fell in layers, within this extinct crater, or circular depression. —

+++ Note Perhaps the most probable source is the Green Mountain. Similar substances are abundant in different parts of the Isd. — the cause of their present position is often ambiguous, which perhaps may be attributed to the action of the winds, at the time or shortly



after their descent, & before their agglutination. — These porous layers, on the Green Mountain collect the water, & by a most fortunate circumstance, a continuous but very thin layer of clay-iron stone 3750, throws out in the form of a spring. — It may be asserted, that the existence of all the larger animals on the Isld. depends entirely on the occurrence of this seam of compact stone. —

The stratum, which I have mentioned, as composed of fine yellowish & pinkish ashes but slightly condensed, is remarkable, from a layer, abounding with spherical balls. These vary in size from a half to nearly three inches in diameter, one inch being the most common measure; they are exceedingly tough & difficult to break; the fractured surface, is very smooth & even; color pale yellowish brown; the fresh surface slightly adheres to the tongue & gives a saline taste; their nature, I apprehend is the same as the ashes, in which they are embedded, only united by some chemical attraction. — The exterior parts of each ball, generally consist of five or six distinct envelopes, but merely separated from each other by a surface similar to the external one. The concentric structure gradually vanishes leaving a homogeneous



nucleus. — In the very centre, a minute irregular cavity may be observed, with some black metallic like specks. 3799. 3800 — Some however of the largest balls appeared to have had a soft nucleus of ashes, similar to the whole stratum. — Besides the spherical form, A very few were had an irregularly cylindrical form with rounded extremities; in the specimen of this kind, which I brought home, the whole interior appears studded with the black specks: may not this be the case absence in of one central point be the cause of this peculiar form? — The balls are exceedingly numerous, so that several in some spots almost touched each other. — I noticed a few, in a layer above this principal one. — In attempting to account for the origins of these bodies, we must first remark, that the existence of successive concentric envelopes, almost implies either a motion, either in the body itself, as in a Bezoar stone in the stomach of an animal, or in the surrounding matter, instances of which may be seen in dripping mineral springs, (as in Puente del Inca in the Andes.) —

Hardness & chemical action in fine ashes

It does not appear clear, how the balls either case alternative could have happened in a bed of soft ashes. — if we give up idea of accidental Yet such must have been the case; it was perhaps owing to 3 successive contractions in the process of consolidation: without indeed we imagine these to be aerial forms produced during the descent of the ashes. — If we give up idea of accident, there only remains contrast. Badly expressed.

Hardness & chemical action in fine ashes] added pencil. 

if we give up idea of accidental] added pencil. 

If we give up idea of accident, there only remains contrast. Badly expressed.] added pencil. 




Recapitulate volcanic formation

There are a few facts, respecting some formations of the present day, which are worthy of being described. — In several parts of the Island there are occur extensive white beaches, composed rounded of calcareous particles. of Near to the settlement where the superficial sand shifts, the lower part is found cemented into a firm stone. This calcareous sandstone is composed of small well rounded fragmen grains, resulting from comminuted shells, corals & other organic bodies. 3751 3752 — the greater number are white, a few some yellow, or pink — in but very few, can any trace of organic structure be distinguished. — Occasionally there is a considerable sprinkling of particles & even of small fragments, of volcanic rocks; but rarely shells are found, this may be explained from the long time such fragments would probably have been would have been tossed about on an these exposed beaches, before the period of their consolidation arrived. Other extraneous bodies, such as turtle eggs v. Lyell &c &c are occasionally embedded. — These stones are quarried & used for building, & as so commonly happens with such freestone, they become much harder from exposure. — It is believed that one year is sufficient for the formation agglutination of the sand. — Besides these freestones, there are other varieties of much more compact, hard rocks: which cannot be worked, some of these are composed of coarse particles; others, of fine. — Of the latter

Recapitulate volcanic formation] added pencil. 

v. Lyell] added pencil. 



I saw strata, about half an inch thick, which were exceedingly hard compact, brittle & sonorous 3753: 54; the rock almost graduated in a compact solid Limestone. Silex? In all these latter varieties, each separate grain of shell, or of volcanic rock, is enveloped in a thin case of pellucid calcareous matter, which thus unites the whole into a solid mass. (a)

(a) Note: I believe in a similar strata at Coquimbo in Chile, the opake central part of each grain, that is the particle of shell has been removed, so as to leave the envelopes, hollow. —

Rarely this cementing matter is stained brown. — Neither The calcareous sandstone does not occur at an elevation greater than that at which gales of wind could throw the sand; hence, from this alone, we may almost conclude, that since the last streams of lava reached the sea, the land has not been elevated. H --------. Lieut. Evans informs me, that the sand on Long Beach, which is directed about NE & SW moves periodically from one end to the other.

Spec fine common Limestone 2.6 Phillips

In the months, included between the end of March beginning of April & beginning of October, it proceeds towards the NE: & from November October to end of March again it returns to the SW. — Carb of Lime [crusty] 2.7 This movement is probably owing to a similar periodical change in the prevailing swell of the sea; the direction of the wind remaining nearly constant. Lieut Evans also informs me, that during the six years he has resided on the Isld. he has observed that, in the months of October & November of each month year, a hard   

Silex? ] added pencil. 

Spec fine common Limestone 2.6 Phillips] added pencil. 

Carb of Lime [crusty] 2.7] added pencil. 



calcareous incrustation appears, on the lava rocks of the beach, near the settlement. The incrustation is hard, white, resembling the nature of the thick shells of molluscous animals & is composed of successive thin layers. It appears gradually & disappears in the same manner, within the time specified [ie] it varies now only coats the tidal rock from close to the settlement & in no other part of this Isld; — it varies in quantity in the different years. —

marble 2.71

2.63 Ascension specimen

In 1831, it was in remarkable abundance; — I found a point of lava, near the stone quarry, which till lately had been covered with sand, it was coated to the thickness of quarter of an inch, with hard calcareous matter, such, as I have described. or degradation 3755 — Mr Evans felt no doubt this was a remnant of the incrustation of 1831 which had been protected from re-dissolution. The settlement is situated close on to the southern end of Long Beach; we have seen that in the same months of October & November in which the incrustation takes place & the sand moves first travels to the SW, in the same months of October & November, in which the incrustation takes place. Must we not believe, that from the disturbance of the sand already perhaps

marble 2.71] added pencil. 

2.63 Ascension specimen] added pencil. 

or degradation] added pencil. 



partially cemented, the water is charged to excess with calcareous matter, which is deposited on he first hard rocks which it encounters encountered by the stream? — I thought this circumstance worth mentioning, as it shows by what singular & trifling causes periodical deposition may happen be produced. —   #

Besides the incrustation already described, there is, in the same locality, & on the tidal rocks another & permanent one on the tidal rocks. Its appearance of this one is most singular 3756 to 3767: [five words in pencil faded and illeg]

the general colour is a dark grey, or pitchy black; & its form may be compared to the Hepaticae, which adhere to hard surfaces in humid places. The layer varies in thickness from one to two tenths of an inch; it consists of a very hard & compact, almost crystalline limestone, which is coloured by some extraneous matter; a particle under the blow pipe, immediately becomes white; & in muriatic acid a very small residue is left. — Oliva's are colourless on underside & under [1 word obscured by tape] The figure which it assumes is that of rounded slightly elevated fronds or discs, which have a [illeg word in pencil] sinuous & crenulated margin. both [illeg] & fragile (in more than one place) — Hence the comparison with the Hepaticae — The usual average diameter of the fronds is about a quarter of an inch;

Oliva's... [1 word obscured by tape]] added pencil. 

both [illeg] & fragile] added pencil. 




their surfaces are tolerably even, & polished to such a degree so as to be glassy, like the most beautiful species of the genus Oliva. — I have occasionally seen the form simply botryoidal, & but fissured; in such cases, where the colour was black, a considerable resemblance to      blistered manganese was apparent. — I do not think, any one would readily at first credit it was a calcareous stone. — These glossy fronds incrust all the points of scoriaceous & compact basalts, which project above the calcareous beach. — As the sand shifts, the force of the waves must alter their bearing; & hence it is perhaps, that the incrustation seems constantly to change; in one part being replaced whilst in another it is worn is wearing away & bears a dull surface. — In examining the specimens which I collected, the first origin of the fronds is seen to arise from a small aggregations in sheltered crevices of the common rounded particles of the beach.  These whilst they are firmly cemented together, but are corroded into very many rugged little points; the individuals grains frequently show a ribbed structure, & the whole on a minutely microscopical scale may be compared to a bold mountain chain. — The summits of these pointed



little patches, presently are worn off; into a smooth & nearly even surface; then, as in a horizontal section of a mountain, the valley would form the greater sinuosities, & the ravines the smaller or crenulated outline. — The water, although a corroding power, likewise deposits the thin glassy coating, which is probably similar to the pellucid envelopes & cementing matter of the calcareous sandstone: It is this, which communicates the colour, as may be seen, when a fragment of shell becomes embedded between the fronds: the intensity of colour depends on the quantity thickness of the glassy coat, hence in the early stages, the white particles are only tinged with the faintest grey. — Mem. Introduce Phosphate Lime. These successive additions, although tending to alter the preceding original figure, must to a certain degree follow the primary curvatures. —


Where this matter is in excess, perhaps the botryoidal form is produced, & in my specimens such are of the most intense & polished black. There is another cause, which must produce a confused blending of the 

Mem. Introduce Phosphate Lime.] added pencil.   

Multipora] added pencil.



fronds; it is that single rounded particles become agglutinated between the perfect & old fronds, & so either form new centres units with, which must soon be united to the neighbouring margins. Hence, in the cross fracture of the incrustation, white spots will commonly be seen.

Mem the parallel but less developed case at St. Jago

I have described these bodies, at considerable length, because I confess I was at first completely puzzled both by their composition & the origin of their forms. —  Mr Horners substance. I am yet ignorant of the nature of  the colouring matter; is it drawn from the dark volcanic rocks on which the fronds adhere? —

Dr Webster (voyage of the Chanticleer) V. Voyage has described layers of salt & gypsum, produced from the spray of the sea; He states that water infiltrating through these substances have formed in a neighbouring cavern stalactites of the latter substance. — Lieut. Evans describes them as very large; some specimens which he gave me were long & pendulous 3768: 69 3817; composed of fine transparent Selenite, in which the concentric layers & vertical crystalline cleavage are both distinct. — Recapitulate Volcanic phenomena. Compact gypsum is also found in caverns remote from the sea. — And salt on the side of Cross Hill oozes through  the scoriae & form considerable deposits, both these substances are, I apprehend, in these cases. Volcanic productions. —   

Mem the parallel but less developed case at St. Jago] added pencil.

Mr Horners substance.] added pencil.

Recapitulate Volcanic phenomena.] added pencil.

953 verso

[The page has a vertical crease which Darwin has used as a separator so that the right hand quarter of the page has separate text from the left hand. Gordon Chancellor.]

[Left hand text]

April 29th 1835 nothing Description of Mr Hennahs specimens from Ascension. Geolog. Proceedings.

Ed. Phil Joun. Jan 1830 account of Ascension

In Coll of Surgeons. A [calculus] from animals stomach. nucleus a nail. The form from it has gone in exaggerating to a remarkable degree which is quite point in case to great branches from minute irregularities in first particle dissolved a wood cut [might] be taken [diagram of nail in calculus]

If structure of sandstone is[discussed]of Coquimbo then R.N p. 61

Alternations of glassy and stony Pearlstones Daubeny R.N 90 & p. 89

Mr Lyell thinks there is silex in black incrustations

{Long discussion on Pumice & Obsidian Vol. I Humboldt

Laminar alternations not effect of coolings

Pisolitic ball RN. P. 72

R.N p 60

R.N p. 3

[Right hand text (right hand edge concealed by archivists' tape?)]

Krusensterns Voyage Vol. II p. [383]1 19th May 1806 Saw a cloud of smoke [surge] Volcanoe [entshroud] Lat 2º 43’ S Long 20º 35’ W Greenwich I suppose

In Voyage Officier du Roi Vol II p [9-]2 during April [May] 1764 earthquake [fall] in Atlantic water 25º W to France I suppose

Scrope p 703 says M de Moreau Jonnes has remarkable effects of trade winds on form of craters

Edin Phil Journal January 1826 Ascension4

1 Krusenstern 1824-7. The several references to 'R.N' are to the Red notebook. JvW

2 Saint Pierre 1773. JvW

3 Scrope 1826, pp. 70-1. JvW

4 Campbell 1826. JvW

This document has been accessed 29048 times

Return to homepage

Citation: John van Wyhe, ed. 2002-. The Complete Work of Charles Darwin Online. (

File last updated 11 July, 2022