To James Geikie   13 December 1880

My dear Sir.

You must allow me the pleasure of thanking you for the great interest with which I have read your Prehistoric Europe—¹ Nothing has struck me more than the accumulated evidence of interglacial periods & assuredly the establishment of such periods is of paramount importance for understanding all the later changes on the earth’s surface.² Reading your book has brought vividly before my mind the state of knowledge or rather ignorance, half a century ago, when all superficial matter was classed as Diluvium & not considered worthy of the attention of a Geologist.— If you can spare the time (though I ask out of mere idle curiosity) I should like to hear what you think of M^r. Mackintosh’s paper illustrated by a little map with lines showing the courses or sources of the erratic boulders over the midland counties of England.—³ It is a little suspicious their ending rather abruptly near Wolverhampton, yet I must think that they were transported by floating ice— Fifty years ago I knew Shropshire well, & cannot remember anything like till,—but abundance of gravel & sand beds with recent marine shells. A great boulder which I had undermined on the summit of Ashly Heath 7203 (?) ft above the sea rested on clean blocks of the underlying red sandstone.⁴ I was, also, greatly interested by your long discussion on the löss;⁵ but I do not feel satisfied that all has been made out about it— I saw much brick earth near Southampton in some manner connected with the angular gravel, but had not strength enough to make out relations— It might be worth your while to bear in mind the possibility of fine sediment washed over & interstratified with thick beds of frozen snow, & therefore ultimately dropped irrespective of the present contour of the country.

I remember as a boy—that it was said that the floods of the Severn were more muddy when the floods were caused by melting snow, than from the heaviest rains; but why this should be so I cannot see.

Note. (I have run short of paper & am away from home).⁶

Another subject has interested me much. viz. the sliding & travelling of angular debris   Ever since seeing the “Streams of Stones at the Falkland Islands—I have felt uneasy in my mind on this subject— I wish M^r Kerr’s notion could be fully elucidated about frozen snow.⁷ Some one ought to observe the movements of the fields of snow which supply the glaciers in Switzerland.

Yours is a grand book, & I thank you heartily for the instruction & pleasure which it has given me.—

Pray believe me. | My dear Sir. | Yours sincerely— | Ch. Darwin

For Heavens sake forgive the untidiness of this whole note.—