RECORD: Darwin, C. R. Geological diary: San Lorenzo. (7.1835) CUL-DAR37.711-715 Transcribed by Kees Rookmaaker, edited by John van Wyhe (Darwin Online,

REVISION HISTORY: Transcribed by Kees Rookmaaker, edited by John van Wyhe 10.2012-3.2013. RN1

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.

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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.


July 27th San Lorenzo


On the Eastern side of Island, there are worn into rather steep side of hill about 3 inclined & narrow steps; these are scarcely discernable excepting when on them. The lowest is [illeg] covered in parts for the length of about a mile with bed of recent shells. The bed is in parts upwards of 2 feet thick, generally less & in places they lie in heaps. The highest point, where they were in numbers was 85 ft above high water mark, from which they were plentiful on a slope. to the edge of a low precipice which forms here the coast line.

The shells were of all sorts & ages mingled together, & such as now may be not with [illeg] the beach. — in this present day I have not noticed so many Crepidulae, which amongst the dead ones is far predominant. — The shells are much

711 verso

no trace of horizontal deposition in shells: generally mixed with a few fragments & but little Earth. —

(a) They The steps are cut out of the stratified sandstone. are irregular & obscure. — Yet certainly steps

The shells are frequently covered by a few miles of soil. —


weathered, bleached & brittle. Yet a few Turbos & a conical small Fissurella retained its olive & red color. — It was curious to observe, how completely discolored both its external & internal surface. — Some of the Univalves, had clearly been dead one, with Balanidae & Serpulae on their insides, generally much broken. — There was also with the shells a good deal of pure cryst salt, probably from the spray of former beach. — These shells rest on an indurated earth, with angular fragments of inferior rocks & shells, cemented by salt & probably Carb of Lime. —

Together with the shells, there were birds bones, bits of roots of sea weed, corallines — ova of Molluscan animals — & other vegetable matter amongst which were the heads & flowers of Indian corn & thread. — From the immense quantity & general appearance, independent of state (& position on edge of precipice no water on Island reaching around a whole belt of the Island

712 verso

(3156) Comminuted shells

(3157) The yellow white calcareous Powder

3158 — 59 Shells from S. Lorenzo

1687 a great Earth quake


3 San Lorenzo

& at least 50 yards wide, & being placed on one of the steps. It is certain this was a sea Beach. — (Moreover Mr Gill in other parts of the Island. there had has seen the same belt. —)

At this period men existed: from a piece of the string I believe Europeans: — — As people have formerlly lived on this Island. & there was piece of water then, it is possible these may have been buried by accident with a dead body &c &c.

I cannot feel sure about these relics as there were stones piled up near the spot. — something might have been buried & ground smoothed over again. —

The shells have the appearance of greater age, then almost any I have seen at [illeg]. Yet the elevation is only 85 ft. Is this owing to subsequent depression. or to pre slower upheaval. —

The climate must at least be as favourable

713 verso

1860 ft


[The image sequence of pages 715-714 is out of order]

for their preservation, as to the South. Parts of the bed of shells are much more decomposed than others. where there are many fragments the shells are almost reduced into the state of a soft white friable earth. — On the 2d shelf 95 above this first or 170 above the sea: on digging through about 6 inches of loose earth, there is a layer of a few inches thick, but varying in quantity of a yellowish white soft powder, this has frequently percolated between the underlying stones: is often saline to the taste, rest on a hardened earth with fragments as below. —

There is not a trace of a shells. Yet I cannot doubt but what this has over been a bed of shells — every circumstance is similar. — Specimens show a gradation in nature. — Therefore the line = to 95 ft elevation has destroyed every trace of structure.

We may conclude when the 85. reached the height of 170. ft. there will be no sign of shells.

715 verso




The highest point of Island is nearly 1200 ft. — in very many of the higher parts I found small quantities of a similar substance. — The observing step is at a considerable greater height. In any other climate where grain would dissolve & stand. & vegetation blacken; such signs could not remain so long. — Yet it may afford a clue sometimes & has always been a desideratum to me. to know what traces would be left.—


30.436 = 30.554 30.454

30.350 = 30:367

1.483 644
1.482 404
0.001 242

= 80.9 = 85 ft high


30.454 & 30.230 = 243


2.227402 = 168 &c = 170

714 verso

San Lorenzo — Lima

July — 1835

Height & shells & calcareous earth. —

Piuia — Puyte — shelly

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File last updated 1 April, 2013