RECORD: Darwin, C. R. Geological diary: Port Desire. CUL-DAR34.29-34 Transcribed by Kees Rookmaaker, edited by John van Wyhe (Darwin Online, http://darwin-online.org.uk/).

REVISION HISTORY: Transcribed by Kees Rookmaaker and John van Wyhe, corrections by van Wyhe and Gordon Chancellor 1.2011. RN2

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.


29

Port Desire

N side of River. Porphyry. —ascending which you arrive at a dead level plain, much divided & cut up by vallies one side corresponds to the other. —

This plain reaches up to the foot of two hills ∴ is seen stretching to the West-ward. to the SW. & South of [River].

all level forming square pieces of table land. — covered with gravel of porphyry. —

endless varieties, & some white quartz. pebbles here the size of R Negro but evidently same sort — all water brackish, more or less. V [Bottle]: is it washing any salt water of old sea? In one valley, which was deep, there was a coating of salt which resembled the Salitrales more to the North. — V. Specimen. — On the high plain, there are groups of many shells lying thick together, & curiously perfect, considering

29 verso

exposure to weather. — Patellae. & Mytilus with colour. — (same as New bay) not covered with diluvium. — recent sea cause of sterility. — I should imagine gravel 10 20 or 30 feet thick, for beneath this there appears a white. calcareo-sandy clay — clayey sandstone in soft. forming beds. seen in vallies at foot of 2 Hills. — same as upper bed at New Bay & R. Chupat. — .

2 Hills — low range of porphyry. generally forming sort of laminae & very imperfectly crystallized. V - - - - — specimen. — compact well crystallized. & the above sort all occurring together. — Porphyry exposed by vallies evidently covered up by the calcareo- sandstone bed. —

Did these hills up-heave. the modern

30

bed or upheaved with it?

On salt side. rough porphyrys. (a white variety same as in cherry garden occurring with the red sort.). — Britannia rock very porphyritic variety. —

Barranca. about 5 miles on S. shore. — 130 feet high. —

yellowish sandy clay. form a bed about 40 feet high. — res many large oyster especially in lower part. — chiefly characterized by Turritella. — & many large Arica. — some Pectens: (a Volut. Buccinium (, which I could not bring home). Above this immense bed of gravel. — line of separation horizontal. — Further inland great level plain, same as the northern, with white calcareo-sandstone. which is above level of gravel bed. — Therefore gravel covers great inequalities in lower modern beds. —

30 verso

Going up Southside of creek. meet many varieties of Porphyry. few miles beyond. Guanaco. Island. I walked into the Interior there appeared to be high table land within. but it really was not evident when approached. — was covered with gravel. & composed of calcareo-sandstone; excessive marks of diluvium. not now accountable & was vallies going east immense barriers (which are exposed) of Porphyry have been cut through. — Near here. ab calc. sandstone crossed lied upon earthy Porphyry (655. 656). —

& was covered by thin bed of ferruginous sandstone: — at extremity of the creek, rock sublimely peaked & perpendicular valley most abrupt sided. — one side valley suddenly commencing with cliff of 100 feet

present stream minute. depositing fine mud on the rock much pebbles: in course of river one boulder of greenstone. — It is certain that cause much more violent

31

than now exist. must have acted. such as Volcanoes. (immense beds of gravel shows same thing). & the plain I think requires same condition. —

At the very head saw square white table land. —

Cliffs on this side of Wood Island. very remarkable: at first the lower part is generally more crystalline such as. (653). — then comes a sandstone with small pebbles. — Porphyry looking like jasper. — more sandstone. — sandstone sometimes largely conglomerate — (what pebbles?). — Such rocks as (653) pass into red rock. — Above the sandstone, not weak separated chalky bed. — Is it same as high land? —

There are many dykes. one running (compass ENE.). — Do they cut the chalk. — Strata irregular. W by S dip most common. — Does the chalk dip? Proportion of beds? nature of superior table land. ? — Salinia. ? —

Dip? Lower rocks? Has there been two upheavals? . double range of table land, lower 50 or 60 feet above sea. — higher some hundred. & some miles further back.: Dykes

[sketch] [sketch]

(1)

31

opposite Guanacos Island. Pitchstone occurring under porphyry. —

Guanacos Island iron stone occurring in Porphyry. [sketch]

J

1)

(2)

The porphyry rock is often cavernous, irregularly papform.

These two hills are composed of the laminated porphyry. — The great plain, at the foot of two hills, is generally covered by calcareous (1640) sandy soft sandstone. — sometimes it is not calcareous 91662). — this seems to lie over a sort of clay. salt taste (origin of salt water?) angular decomposition (1663. 1664) which contains layers of fine crystall: gypsum. — it is probable that the oyster beds belong to this plain; although not been on north side.

The South Barranca (I saw. Jan 4th) are horizontally stratified; the clay bed is half the thickness of cliff. — the gravel other half & the cliff about (80 feet) or less than quarter the whole range, high plain, where we have seen Calc. sandstone. — The organic remains, in the bed & the gypsum in upper part show it to be of same age as great St Fe bed. — Area greater size. — Turritella more numerous. — but yet same general feature. — the calc. sandstone appears to be the same as occurs above oyster beds at R Chupat & New Bay. —

On the — this connects

The 2 & 8 [illeg] cliffs south west of the ship are curious, they are essentially composed of feldspathic rock, but alternate & pass into each other incessantly. —

The common rocks are white hard feldspathic (672. 673. 679.) They generally rest on such as red, hard. porphyry (674). — which occasionally becomes more crystalline as (677). — There are no limits to these alternations & passages. Another perhaps even more abundant rock a common feldspathic rock 1649, where the universal occurrence of very small rounded pebbles proves the action of water. — this is covered by such (674. 647. 1648 red porphyry: jasper porphyry, white [illeg] held. rock 1665 1650). — The sup more common superior bed is a rock, resembling ferruginous sandstone, but really a soft earthy snow white thick bed with particles of quartz. strikingly resembling calcareous matter. as (1651. 1675). Then the white & red, fine grained, uncrystallized feldspathic rock. —

(2)

31 verso [blank]

32

(3)

The colouring matter of the red varieties, often times tinges the white of a delicate pink sometimes in lines. — at other times, in a horizontal section. in circular patches & parallel bands of white occur in the midst of the red. — V curious drawing on a small scale. —

Following section will illustrate

  Gravel   Gravel      
  Dip NW   Dip NNW      
1 rock like 1683. without water lines   1683 (like) 1647. 1648  
2 same as 3 but much coarser   1668      
3 (1651) like mortar   1667 (like)    
4 1674 (like)   1647 (like)      
      666 & like      
      1674 (like)      

all same dips

  1669   1674   1677 pebble
1667   1647. 1648   1672. 1673 like 1650  
1668   1649. like   1674 like      
1666   1653      

1678. 1679

coarser variety with pebbles

 
               
               

 

[sketch]     well separated
1651   1766. 1765 East entrance
1681   1766 cliffs
(1674. 1649 like)   1767  
    1768 clearly junction mark as in F
       

These rocks are traversed by dykes. of which I found three.

1st had even sides, straight & vertical & composed of the same substance as the surrounding mass, which was (1649), the central parts. were tinged red. — must be fissure filled up. —

The two others were vertical, very tortuous & might be traced for long distance. — it the 2d was composed of rocks such as 1652 & 1672; about a foot thick — I could not perceive it altered the rocks. — it cut curious chemical nature

(3)

32 verso

(4)

all the beds, untill impeached the earthy feldspar, like 1651 & others something like 1683. — 3d & thus [sand] in a NE & SW course an E & W course. — the 3d dyke was composed of rock (1670) with much mica & ran S & N — a small dyke of this nature cut through dyke 2d. —

In one or two places there are conglomerate beds beneath such rocks as 1649. — 1672. 1673. 74, always of a dark red colour. — they are composed of pebbles of a size of sand to that of a mans head. — The pebbles are of highly crystalline porphiries such as do not now exist near here. — They have been deposited in rapid current. from the stratification, general dip of beds same as usual. — From this & such specimens as (1783) with water lines I conclude all these rocks have been formed under water. — If I had only seen a section such as F. I should have thought (1677) had been melted & poured over the inferior rocks. — more especially as the junction is slightly inducted. — Whatever origin of 1679 is It must be the same for all porphiries 1634 -- 39. for where section F is; the cliffs end & great porphyritic formation begins of which (1677) present in external form & nature a good type. — Yet I cannot think rocks such as 1681. which pass into 1675. & such, 1673.,. 1674. which lie over rocks of aqueous origin such rocks as 1673 passing into. 1649 & pass into each other & alternate without marked change can owe their origins to such different causes as Fire & Water.

Section F is interesting, where Porphyry 1677 dips into the sea.

I thought it belonged to the range of hills behind the Fort — it was only at its outcrop. I saw it overlying such rocks as 1678. 1679.) & other coarser varieties with small pebbles such as (1649). — The dip is here W N W. — which is unusual & it is the point of a bite or bay & commencement of the tw softer rocks. —

(4)

33

(5)

The general dip of all the above rocks is NNW. — but not accurately; the stratification is in plains considerably disturbed. at Dip at about 15°. —

I noticed here the same fact as at the Falklands namely outcrop behind outcrop without anticlinal lines. —

[sketch of anticlinal lines]
11m
Gran 1650 1675
Mortar
white [illeg] 1681 1650
1674 Red [illeg] 1649
1651 mortar & F.B. 1681
Red Porphyry
1674 1649
1677
1678. 79

I may notice that form of harbor roughly agrees with stratification. creek running to the S. of W & E. —

In the East of the Fort, where the Spaniards have quarried.. — The following rocks are visible. —

1682 —— to 1691. — which tell something like same tale as section F. viz. that Porphyry (1684) (which is part of same bed with (1690: 1691) & which include the principal varieties in the country. lies over rocks of a very earthy nature, sometimes quite soft. & very commonly lined with horizontal or waving ferruginous lines. as in sandstone, evidently formed in water. —

    1684
1682   1685
1683 > 1686
    1687
    1688
    1689
    1683 (like)

These 6 rocks occur without any determinate order & pass into each other. —

The passage of Porhyry 1684. is certain. the laminated variety 1691. occurs at top of bed. — which appears to be its common position. — These beds (porphyry) inducted dip to SSE at ∠ 10° (or about). now they rest

(5)

33 verso

on S side of great Porphyry range. behind the Fort. —

This range runs about ENE & WSW or NE & W. which line continued falls to the South of the cliffs. & therefore their northerly dip is explained by line of violence continued, although no actual hills are produced.

The following facts are I think proved by geology of Port Desire viz that earthy & crystalline porphiries were formed, were covered by conglomerates & other mechanical rock; that rocks partaking of both character of mechanical & chemical passed into each other & alternated an argument for the Wernerians; that there was a common deposit of white earthy feldspar: & that the dykes are of curious chemical nature, that the conglomerates are formed from the rolling of porphyries rocks now present.

that these beds were upheaved by the chain of hills north of the Fort. — That this roughly impressed the present form of land. — That in certain places, a great bed of yellowish sandy clay was deposited abounding with large ostreae very generally same fossils. with S Josef & St Fe ∴ contemporaneous.

that the upper parts of this bed was purer clay & contained layers of Gypsum, that above this there is bed of to earthy sandstone, sometimes generally (same as in R. Chupat near Rios calcareous. — That these beds show no sign of violence. — That after this a most enormous alluvial action removed parts of the lower beds & deposited a vast thickness of rounded porphyry & white quartz pebbles. (if these were two upheavals one took place at this period?) — that the sea remained or this gave time enough to leave shells which now exist, even with their colours. elevated 247 feet above the sea. — Then the land was elevated or sea subsided. — That some this there has been very great alluvial action, more than the present dry climate

6

34

(7)

can account for. Even if we put out of the case the great removals & immense vallies in the upper plain, where there are little traces of water ever running.

We may instance the creek, which cuts through hard Porphyry rocks, 100 to 200 feet high, nor only a little stream with which deposits mud. — Leaving about pinnacles & overhanging crags, as a mark of former. — I saw one of the rude precipitatious side ravines, commencing at once, with a cliff 60 or 70 feet high, as in volcanic country.

I think volcanic earthquakes must here have been present, & aided by rapid torrents. — Would not old creeks, where is shown to exist in the harbour, when covered by modern beds yet be the lowest part & account for modern vallies coinciding with old ones. & these, leaving one to suppose present causes had effected them.

when in such a case of this shells with their colour reducing you to a short period, renders it impossible.

 

[illeg] gravel many

from [2 words illeg] shells rounded from the beach & mud from [illeg] with [illeg] bones.

Then upheaval

34
18
.190

.492
190
.302

214
190
.024

[illeg] 30 32
.164 in same hours.

4 3/4 7 = 10/4 7 = 19/28 of .164. = .111

28/ 3116 (111)
28
311
78
36
28

19
1478
1641
19 31 16
19
121 (19)

160
28
1312
328
459
38
79

(7)

34 verso

supposing to conflict or

Porphyry & modern beds upheave upheaved together (proposing a foot or two this N. plain)

(Superposition of gravel. —)

(Age of bed. calc. sandstone)

Port Desire

Jan. 1833

 

2. stratification & dip

1. General origin. — age &c &c

Porphyries up harbor &c

Great modern bed. (Elevation of plain, height &c

Sterility salt water

Vallies &c old system

(Gravel above (Oyster & Porphyries)
Port St. Julian

Nature of gravel [sketch]

(Change in life from gravel

The gravel not very long after the Argilla being then not very darker for clay beds from Oyster being found higher up. — Yet after the deposit of gravel complete change of life. — modern shells inland of Pectens Julian & where

It would appear to be a [Calanote] over the than species on the right & being replaced by other sorts

[Turions] (shells from coast) Patella, Muscles


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