RECORD: Darwin, C. R. Geological diary: Peninsula of Lacuy. (1.1835) CUL-DAR35.304 Transcribed by Kees Rookmaaker, edited by John van Wyhe. (Darwin Online,

REVISION HISTORY: Transcribed by Kees Rookmaaker, corrections by John van Wyhe 5.2011. RN1

NOTE: Darwin's time in ChiloƩ is described in the Beagle diary pp. 280-6. This document is the continuation of the description of Chiloe, Dar35.288-304. See a map of Chiloe from Narrative 2.

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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.


1835. Jan: Peninsula of Lacuy (15)

From a more extended examination of this part I have the following observations to add. — The general formation may be considered as consisting of very numerous alternations of brownish sandstones (a), alternating with (2514) with greenish or grey slatey clay. The sandstone chiefly contains the extraordinary concretions; it also passes into the finer grained yellow fusible substance & the brecciola with of white pieces, already described. — This difference, of the beds from the general character of the rest of Chiloe (I have no doubt is rightly attributed to the proximity of a former volcano. p.17 mica slate

Perhaps in a similar manner, the slight difference observed at Castro may be connected with the existence of the trachyte columns. — I have already alluded to veins of agate &c. these fill up fissures, which traverse generally in rectilinear lines the sandstone. The agate or siliceous stone often seems intimately connected with the surrounding sandstone; where it is not present the sides of the fissure are generally harder, so as to project: this would appear to be from subsequent infiltration. — The fissures have been formed during anterior to the arrangement of the particles of sandstone.

In Diagram (B) we have a horizontal section of yellow sandstone 3 or 4 ft x 2 ft, crossed by numerous & generally rectilinear lines of fissures (a); the sides are represented by the double lines, which are slightly prominent. —

The curved lines show on a side the figure of the arrangement of the variously sized & colored particles in the sandstones; the number of these alternations are not attempted to be shown. — A similar appearance is often seen in horizontal layers, of variously sized sediment. — it was is here from the form very [sentence unfinished, continued in DAR35.310]

304 verso

(a) which cut each other at high angles

(b) which very rarely have a pebble, excepting in those places where the whole mass passes into the conglomerate or alluvium, often mentioned. —

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

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