Wants AR to make any observations she can on the occurrence of little ledges on the side of steep, turf-covered slopes. Feels they may result from the washing down of worm-castings.
9 Devonshire St | Portland Place
My dear Amy
I want you to observe another point for me; so you see thatI treat you as my geologist in chief for N. Wales.f1
The late Prof. Henslow,f2 who was a very accurate man, said thathe had often observed on very steep slopes, covered with fine turf,(such as may be found in mountainous countries & no where else)that the surface was marked by little, almost horizontal, sometimessinuous & bifurcating ledges; or as he called them, wrinkles. Theseare commonly attributed to sheep walking in nearly horizontal linesalong the sloping surface; & they are undoubtedly thus commonlyused by the sheep; but Henslow convinced himself that they did not thusoriginate. Dr Hooker, to whom Henslow made these remarks, has sinceobserved such little ledges on the Himmalayah & Atlas ranges, in partswhere there were no sheep & few wild animals—f3 Henslow speculatedthat the earth beneath the turf was in some manner graduallywashed away; & he compared the wrinkles on the turf to those on theface of an old man whose face is shrunk. I cannot possibly believein this notion.
Would you look at any very steep grass covered slopes near you,& if you can find any appearance such as I have described, will youmake for me an eye sketch on some approximate scale of the relativeappearance & distance of the ledges. I have been speculating whetherthe ledges can possibly be due to the washing down of the wormcastings, & their union into little ridges, on nearly the sameprinciple that when the wind drifts loose sand, it makes numerouslittle ridges at right angles to the course of the wind.
You must not give yourself much trouble on this subject, butI shd be very much obliged for any observations or remark.
yours very sincerely | Ch. Darwin
If you find anything of the kind observe whether there are worm-castingson the slope.— Also whether the earth is bare & exposed beneaththe little ridges or ledges.—