I received your letter the other day, full of curious facts, almost all new to me, on the coal-question. (553/1. Sir Joseph Hooker deals with the formation of coal in his classical paper "On the Vegetation of the Carboniferous Period, as compared with that of the Present Day." "Mem. Geol. Surv. Great Britain," Volume II., pt. ii., 1848.) I will bring your note to Oxford (553/2. The British Association met at Oxford in 1847.), and then we will talk it over. I feel pretty sure that some of your purely geological difficulties are easily solvable, and I can, I think, throw a very little light on the shell difficulty. Pray put no stress in your mind about the alternate, neatly divided, strata of sandstone and shale, etc. I feel the same sort of interest in the coal question as a man does watching two good players at play, he knowing little or nothing of the game. I confess your last letter (and this you will think very strange) has almost raised Binney's notion (an old, growing hobby-horse of mine) to the dignity of an hypothesis (553/3. Binney suggested that the Coal-plants grew in salt water. (See Letters 102, 552.) Recent investigations have shown that several of the plants of the Coal period possessed certain anatomical peculiarities, which indicate xerophytic characteristics, and lend support to the view that some at least of the plants grew in seashore swamps.), though very far yet below the promotion of being properly called a theory.
I will bring the remainder of my species-sketch to Oxford to go over your remarks. I have lately been getting a good many rich facts. I saw the poor old Dean of Manchester (553/4. Dean Herbert.) on Friday, and he received me very kindly. He looked dreadfully ill, and about an hour afterwards died! I am most sincerely sorry for it.
LETTER 554. TO J.D. HOOKER. {May 12th, 1847.}
I cannot resist thanking you for your most kind note. Pray do not think that I was annoyed by your letter. I perceived that you had been thinking with animation, and accordingly expressed yourself strongly, and so I understood it. Forefend me from a man who weighs every expression with Scotch prudence. I heartily wish you all success in your noble problem, and I shall be very curious to have some talk with you and hear your ultimatum. (554/1. The above paragraph was published in "Life and Letters," I., page 359.) I do really think, after Binney's pamphlet (554/2. "On the Origin of Coal," "Mem. Lit. Phil. Soc." Manchester Volume VIII., page 148, 1848.), it will be worth your while to array your facts and ideas against an aquatic origin of the coal, though I do not know whether you object to freshwater. I am sure I have read somewhere of the cones of Lepidodendron being found round the stump of a tree, or am I confusing something else? How interesting all rooted—better, it seems from what you say, than upright—specimens become.
I wish Ehrenberg would undertake a microscopical hunt for infusoria in the underclay and shales; it might reveal something. Would a comparison of the ashes of terrestrial peat and coal give any clue? (554/3. In an article by M. F. Rigaud on "La Formation de la Houille," published in the "Revue Scientifique," Volume II., page 385, 1894, the author lays stress on the absence of certain elements in the ash of coals, which ought to be present, on the assumption that the carbon has been derived from plant tissues. If coal consists of altered vegetable debris, we ought to find a certain amount of alkalies and phosphoric acid in its ash. Had such substances ever been present, it is difficult to understand how they could all have been removed by the solvent action of water. (Rigaud's views are given at greater length in an article on the "Structure and Formation of Coal," "Science Progress," Volume II., pages 355 and 431, 1895.)) Peat ashes are good manure, and coal ashes, except mechanically, I believe are of little use. Does this indicate that the soluble salts have been washed out? i.e., if they are NOT present. I go up to Geological Council to-day—so farewell.
(554/4. In a letter to Sir Joseph Hooker, October 6th, 1847, Mr. Darwin, in referring to the origin of Coal, wrote: "...I sometimes think it could not have been formed at all. Old Sir Anthony Carlisle once said to me gravely that he supposed Megatherium and such cattle were just sent down from heaven to see whether the earth would support them, and I suppose the coal was rained down to puzzle mortals. You must work the coal well in India.")
LETTER 555. TO J.D. HOOKER. Down, May 22nd, 1860.
Lyell tells me that Binney has published in Proceedings of Manchester Society a paper trying to show that Coal plants must have grown in very marine marshes. (555/1. "On the Origin of Coal," by E.W. Binney, "Mem. Lit. Phil. Soc. Manchester," Volume VIII., 1848, page 148. Binney examines the evidence on which dry land has been inferred to exist during the formation of the Coal Measures, and comes to the conclusion that the land was covered by water, confirming Brongniart's opinion that Sigillaria was an aquatic plant. He believes the Sigillaria "grew in water, on the deposits where it is now discovered, and that it is the plant which in a great measure contributed to the formation of our valuable beds of coal." (Loc. cit., page 193.)) Do you remember how savage you were long years ago at my broaching such a conjecture?
LETTER 556. TO L. HORNER. Down {1846?}.
I am truly pleased at your approval of my book (556/1. "Geological Observations on South America," London, 1846.): it was very kind of you taking the trouble to tell me so. I long hesitated whether I would publish it or not, and now that I have done so at a good cost of trouble, it is indeed highly satisfactory to think that my labour has not been quite thrown away.