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Lyell. April 16 /56 tells me of the fossil shells found in Madeira & P. Santo, only one common to Europe & that now extinct in Madera. ⸮altered?!. This might be explained in these very ancient deposits from all formerly introduced having been altered — There a & it gives reason to suspect that the 5 or 6/100? now common to the archipelago & Europe may all have been transported into the isld by man; on other hand (& this is good to me) Wollaston thinks some now fd on very alpine summits cannot have been transported to man: these which are identical, are identical because not changed.— It is very remarkable that the 11-13/100 now identical between P. Santo & Madiera, were nearly in same proportion in the very ancient calcareous

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The spreading of imported organisms from other climates is admirable proof, how much more the spreading depends on mastery over other organisms, than on sort of climate

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beds.— much larger proportions than of those common to Europe.— But Lyell remarked that it is most strange considering how much limestone imported into Madiera, that very many more species shd. not now be in common with to the 2 islands— I think it must be that they are adapted to nearly same conditions & organisms, & therefore the Madera species can hold their own. (this bears most importantly on Galapagos & all other similar cases). Thus if isld. off near La Plata had thistle & cardoon, it wd be incredible that it wd when introduced have spread as thistle plant have done: it required an plant adapted to wholly very different conditions or rather organisms, & with having some unknown, great

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advantage over other the aboriginal species then to spread.— Moreover it is very important to bear in mind that H. Wollaston now inhabits only one mountain in P. Santo. & is found fossil at fort.— This shows sometimes how little migration a species mollusc has.— & most wonderful the fact is.—

occupation even less probable than in plants.—

N. B some of the Helices are so peculiar in Madiera that one was described by Bowditch as a a marine Delphinula, now called Helix delphinula.— so with the Cochlearia[?] in St. Helena.—

The Helix Macandrewi is believed to be only land shell on Salvages; Wollaston thinks may be var. of H. pisana fd. in Canary, Azores, & having a wide range generally.—

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Lynnaeus truncatellus? is now spread all over isld. in every puddle; yet I think very few water birds. Good as showing means of dispersal.

The question is, — can the shells in P. Santo be descendants from very few introduced from Europe & from rather more from Madiera.— Lyell's Manual Edit of 1855 p 229 variation of Cardium.

Something about Corbula pisum by Forbes in Eocene of Isle of Wight, soon to be published in Geological memoirs.—

References:

Bowditch, T. Edward. 1822. Elements of conchology: including the fossil genera and the animals. Paris and London: Treuttel and Würtz.

Forbes, Edward. 1856. Memoirs of the Geological Survey of Great Britain, and of the Museum of Practical Geology. On the Tertiary Fluvio-Marine Formation of the Isle of Wight. London: Longman, Brown, Green, and Longmans.

Lyell, Charles. 1855. A manual of elementary geology. 5th ed. London: John Murray. [signed] CUL-DAR.LIB.391  PDF