My dear Sir,

I really do not know how to thank you enough for the immense trouble which you have taken.¹ You have attended exactly and fully to the points about which I was most anxious. If I had been each evening by your side, I could not have suggested anything else. I have been particularly glad to read about the collection of particles of the castings washed down the slopes in the little ditch by the road side & also on the weight of the castings collected by you on a given area; for I have collections made during a whole year on a yard square in England, and can now approximately compare the quantities.—² I do not think it would be worth while for you to keep the whole mass; but I should certainly like to see a few of the common cylindrical castings to which you refer. If M Gény³ knows the name of the common worm which makes them, I should be glad to hear it.— Pray give him my most sincere thanks for his offer to send a collection of the species: but it would be superfluous, as I have not time to enter on this difficult study:—I wish I had the time. My point is solely the amount of earth brought to the surface, and the bearing of this agency on denudation. I hardly yet see when I shall have time to put all my copious notes into order; but I will some day if I live.⁴ I have written to Australia to hear whether the worms work there in that dry country.⁵ Our observations agree in by many points. If there is a long spell of dry weather at Nice pray observe whether the castings disintegrate into dust. I have never seen an instance of this.— It is surprising what little power alternating frost and thaws have on their disintegration.

Heavy rain and wind, whilst the castings are fresh, are the most efficient means in spreading them out on a level surface, and downwards on a sloping surface. They flow like paste a little way down a slope,—about $\frac{2}{3}$ or $\frac{3}{4}$ of the castings being commonly below the apertures.— Perhaps you will attend to this point, and to the approximate angle of the slopes.— As far as I have seen worms do not drag down leaves, stalks &c into their holes, which are used for the ejection of the castings. I cannot conjecture what their object is, or for the collection of large stones over their holes.—

I thank you cordially for your invalueable letter.— What a careful observer you are! I am truly glad your health is better.—⁶ I am a confirmed invalid, and shall never be better till I am in my grave; but I can walk some hours daily, and am then happy.

Yours very sincerely | Charles Darwin