RECORD: Darwin, C. R. [Coquimbo notes]. (5.1835) CUL-DAR39.152 Transcribed by Kees Rookmaaker, edited by John van Wyhe (Darwin Online, http://darwin-online.org.uk/)

REVISION HISTORY: Transcribed by Kees Rookmaaker, corrections by John van Wyhe 3.2011. RN1

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Reproduced with permission of the Syndics of Cambridge University Library and William Huxley Darwin.

See the introduction to the Geological Diary by Gordon Chancellor.


151

May 31st [1835]

252 ft   This expresses the height of plain where quarries are, their plain, none are higher
30.130 TA 57°
30.400 TA 64°

On road, a little South of the City, there is a small valley in grand plain, in which two quite low plains are seen, on botyh of these an abundance of recent shells: doubtless correspond to 2 lowest of town of Coquimbo. —

In the main plain just above there is a pap small grained granite associated with some dark hornblendic porphyries. = I found all the Losa, dip as the coarse freestone made of pebbles of shells is called, & overlying tosca dip to, as nearly as possible at 10°. — the ground here in furrows, I suppose elevation? —

Further to East than [quarries], the formation appears horizontal. — The tosca rock, especially the stalactiform kind forms thick veins, as wel as cap to the Losa. = The surface of the tosca, where barometric meaurement was made, was covered by fragments of blue Mytilus & pieces of Conchlepas; now Conchlepas is very rare in the tosca, as is Mytilus & never blue: yet shells in tosca are I certainly believe, recent: In the conglomerate, which cover the little [illeg] of plain in Herradura.

151 verso

& which is cemented together by calcareous matter, must be of a date posterior to elevation of upper plain. Hence we have absolute identity with shells on beach, & some with partial color: The Calyphnaea striated from the crown is conspicuously common & the common pecten. =

The Losa, on its inferior margin, of no great thickness perhaps 20 ft. blends with & [paints] by calcareous matter, a finely cemented coarse aggregate of broken shells: in parts more or less arenaceous: in some of the sections, these almost consisted of different species of the family of Balanidae, with fragments of the common pecten: in another spot these were associated with great numbers of small oysters (diff. spec: from great). (some of which were yet adhaering to vast contained angular blocks of hornblendic rock)

The shells here are partially silicified altered: there occurred a part of bone in same slate with the hard shelly rock. there were strata of yellow & brown very fine & sometimes aluminous sandstone: oft some beds with much iron rust. —

151a

These & the rock. contained numerous line. & scattered pebbles: (an increase of these is the only difference where Big Oysters were found in a coarse conglomerate). — We see in these strata a mineralogical blending, as well as zoological blending of shells: the small oyster is not known here: also the tosca has not the commonest shells now found here: these specimens 2791—7 were found with Big Oyster & crenated Mytilus. so are though both rare: hence they belong to oldest bed: yet may appear same with my intermediate: a large muscle is common to lowest bed & intermediate:

The pecten is common to all three. —

although I have not specimen. — I do not consider it possible to mark any line of distinction; the shells on surface same as Beach lowest shells most different: a gradation between those:

Lowest beds a compact soft fine grained ferruginous sandstone here without concretions: —

Proof of small valley formed by sea [sketch] vertical old cliff with fringe a yard thick in parts of more recent sticking to it. — : Tosca, all the shells. I know — shelly rock may same (no Quintero [illeg]): Lowest very few I knew. =


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Citation: John van Wyhe, editor. 2002-. The Complete Work of Charles Darwin Online. (http://darwin-online.org.uk/)

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