To Charles Lyell [21 February – 4 April 1841]1
My dear Lyell
I will write down my answers as I read Chiloe is 100 miles long. (I believe I said 90 in Journal2 )— Channel between Chiloe & Cordillera, about 25 miles wide, with some isld.— Soundings were carried across only in one place in line of islets where greatest depth was 95 fathoms— Some highest points in Chiloe were estimated at 3000 ft—general heigt much less In mentioning blocks on Chiloe put granite first, because I know more certainly that syenite came from Cordillera so that your sentence will be more accurate.3
If you choose you may add that the blocks are strewed on shores of islets & in narrow creeks on coast of Chiloe, where there must formerly have been channels, which after hypothetical elevation would correspond with those of Agassiz in interior valleys of Jura—4 I give these facts in paper which I hope to send very soon to Soc.
Chiloe consists of stratified shingle & boulder formation & horizontal strata of tertiary sandstone & volcanic grit—with two volcanic regions & West coast of Mica Slate
There are no fossils with Chiloe boulder formation—only on them—5
Are you sure there are perched rocks on Jura ? My impression (I am not up to looking so I return Agassiz) there are not—that the surface is rather uniform.— The perched rocks if on pinnacles would be to my mind fearful argument for Agassiz’s sheet of ice.—6
Do not you think it worth stating that Agassiz himself seems to consider the angularity of Jura fragments a difficulty on ordinary moraine or glacier action—7
If I were you, I think, I would not give hypothetical union of the two kinds of action,8 but would leave the alternative cases, as you have put them—though I daresay your view is very probable.
Yours most truly | C. Darwin
Excuse this untidy note: my talk with R. Brown after that with you has knocked me up a little
Answers a number of queries from Lyell concerning geography and geology of Chiloé Island and its relationship to the Cordilleras.
Asks about "perched rocks" on Jura and notes their relevance to Louis Agassiz’s theory. Discusses Agassiz’s view on Jura.
Mentions seeing Robert Brown.
Notes R. I. Murchison’s discovery of shells in central England.
Weakness of negative evidence.