RECORD: Darwin, C. R. Geological diary: Santa Cruz. (4.1834) CUL-DAR34.122-124 Transcribed by Kees Rookmaaker, edited by John van Wyhe (Darwin Online, http://darwin-online.org.uk/)

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

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.

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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.


122

(1) April 14th [1834] — Santa Cruz.

The cliffs are 350 feet high. & essentially composed of pale faint yellow, soft partly indurated sandstone. The lower part bed of this is blackish & harder & contains very many shells, broken & irregularly placed: in general appearance resembles South Bananca at P. Desire & in concretionary sandstone in its Turritella. Arcae & Venus. — Pectens I saw none or Balaenidae or Spatangus. — Ostreae are present but not very numerous. Even here there are some veins of gypsum & curious salt: — (Z). —

Above this. the upper part in most cases is partly divided into three varieties: the lowest & superior of which are the same, consisting of pale earthy sandstone — divided into numerous horizontal layers, which are also shown by ferruginous bands: there is a sort of cleavage. — contains these interlaced veins of gypsum. — & large concretionary masses of ([blank]). — & others, but very few slate: The central part is much more shells are infrequent, yet some are present. ([blank]). — The central part is harder — more compact, less stratified, is peculiar by containing in lines which large round concretionary masses of ([blank] These also occur in the superior & inferior varieties: while very generally specimen rocks contain shells. chiefly Venus

122 verso

I believe Isocardium of R. Negro is Arca

Some Gypsum is present when shells exist

(Z) The salt (146 tin label occurs more or less pure (sometimes snow-white in veins running in every direction, oftentimes with gypsum. (N.B. The gypsum has very often been insufficient to fill the veins hence ([sketch]) this appearance). — Salt lies, in the veins in a most lightly uncompressed form, is common in the earthy sandstone. (V. specimen). just above most shelly stratum: — Specimen must contain much impurity

(Mud from grinding of pebbles.)

Similarity of hypogene metamorphic trappean & volcanic rock over whole world all [anser]

123

(Z). I should think between 5 & 600 feet above the sea. — : from an escarpement (like chalk) to the 350 plain. — it is about 8 to the SW by W of present cliff. — but not nearly so far from the sea coast ∴ to which this 350 plain only forms a step: We may imagine as present causes has made cliff A. leaving (D), low. so in old times the (350) plains lose to escarpement (Z): — a double elevation: —

[sketch]
(low) (B)
R. [illeg]
SW now 350 ft
A
high table land (Z)

Extent to the south. &c
Modernness of earthy covering of lower plain as compared to gravel of the upper

123 verso

(3)

bone bed: (without tosca rock)

Perhaps 15 feet thick Does it represent E. T. del F. [East Tierra del Fuego] alluvium? — On the surface there were many modern shells, chiefly blue striated Mytilus. Also one Buccinum. — — Plain level: irregularities caused by the earth. — Some miles South other set of plains; considerably more elevated & with sloping cliff. (Z) —

Features of country as before. —

From inspection of chart, doubtless these formations extend to N. shore of Gallegos. —

The relation of E. T.del F. & this is problematical: this is not present: ∴ either it never existed or has been denuded: in favor of the former is the necessary change in sea. from great gaps in W. mouth of Magellan & the entire absence of porph. pebbles, but it is more probable it only extended in a very lessened degree. to near St of Magellan (v not further south or surely in such quiet deposit some pebbles would be present) & than it was their course washed away — during the depositions of the coarser sort & hence has left larger pebbles at C. St Ines: (my sounding notes. make me skeptible about form of ordinary tides having sufficient power: —

or it is buried deep beneath the alluvium. — probably, hence pebbles. —

124

(4)

These masses are even 3 or 4 (even more) feet in diameter. Are arranged in straight lines for long distances (Z) & oftentimes 5 or 6 2 or 3 yards apart. At other times closer, & vary in size. —

It is clear. that where a layer containing calcareous (?) matter was deposited: such particles united to form these balls. — therefore there was chemical motion in a rectangle [sketch]

It is impossible not to be struck with the resemblance of these beds with those of E. T.del F. viz (especially concretionary masses. of calcareous sandstone)

The difference of shells & gypsum also of pebbles at once separated them. — Yet, perhaps the approximation to same class of mountains is same cause in both. —

These beds with gypsum & few organic remains clearly represent the two at P. Julian & Desire:

Above this formation are the porphyry pebbles 20 or 30 feet thick. (perhaps rather less than to North. essentially the same. St Julians yellow one: I fancy more black ones: —

Above thus in most places this was a bed of earth, with few pebbles. somewhat like St Julian

124 verso

Many of the pebbles were far size of large potato. — I saw a few on beach (St Julian yellow sort) as large as half mans head. —

(Z) The globular form is the rarest: generally this [sketch]: which when close have united forming this [sketch]: oftentimes it is nearly a layer or strata [sketch]: when so small thin & [illeg] & close: —

In the great central bed, there are several layers lines of balls one above the other: Balls formed of concentric layers: —


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