Mexican specimen of laminated obsidian.
Comments on Forbes's publication comparing lava streams and glaciers. Mentions ice-action theories of a young German.
Down near Bromley Kent
I had intended answering your very obliging note sooner, but have been prevented doing so. I am sorry I cannot break the specimen of zoned obsidian as it is not by own; but I should so much like you to see these specimens, that I have taken the liberty of paying the carriage & sending by steam-boat to you, directed to the University 14 fragments of rock, which even if not worth looking at, can not give you much trouble. One is apt to overrate the interest of anything one sees oneself, & I have no doubt I have done so, yet I think the series curious, as showing such perfect lamination or rather separation of minerals in parallel planes, in a pile of rock of undoubtedly volcanic origin.—
I think the Mexican obsidian, zoned with minute air-cells will interest you. Two of my
specimens show the passage from obsidian into the intercallating feldspathic rocks, in
which the laminar structure is chiefly rendered apparent by concretionary action; in the
other specimens the laminar structure is redered apparent by crystalline
action.—: one of these like gneiss appears to me interesting. All the
specimens are labelled.— You can return them, whenever you like, directed to
me to my Brothers House at
I have forgotten to thank you for sending me your latest contributions on
glaciers: by a singular chance, the very day, after I had
written to you, I received the Edin: New Phil. Journal & there read your remarks
on the comparison of lava-streams & glaciers; which if
I had seen sooner, I shd
Believe me, My dear Sir. Yours very faithfully C. Darwin
- f1 790.f1This date is the first Wednesday the 13th after the letter to J. D. Forbes, 11 October .
- f2 790.f2Three of J. D. Forbes's papers on glaciers from the Edinburgh New Philosophical Journal for 1844, bound together and signed by Forbes, are in the Darwin Pamphlet Collection–CUL. They include J. D. Forbes 1844, see n. 3, below.
- f3 790.f3J. D. Forbes 1844.
- f4 790.f4See letter to Adolf von Morlot, 10 October .
- f5 790.f5Presumably CD enclosed a copy of ‘Notes on the effects produced by the ancient glaciers of Caernarvonshire’ (Collected papers 1: 163–71). The passage CD refers to may be: ‘how it comes that the glacier, in grinding down a boss [dome-shaped rock] to a smaller size, should ever leave a small portion apparently untouched, I do not understand’ (p. 165).