18461878] MISCELLANEOUS 2I/ 



in the amount of nitrogen at different depths in the superficial Letter 551 

 mould, and here worms may have played a part. I wish that 

 the problem had been before me when observing, as possibly 

 I might have thrown some little light on it, which would have 

 pleased me greatly. 



VIII. MISCELLANEOUS, 1846-78 Letter 552 



The following" four letters refer to questions connected with the origin 

 of coal. 



To J. D. Hooker. 



Down, May [1846]. 



I am delighted that you are in the field, geologising 

 or palseontologising. I beg you to read the two Rogers' 

 account of the Coal-fields of N. America 1 ; in my opinion 

 they are eminently instructive and suggestive, I can lend 

 you their rcsumt of their own labours, and, indeed, I do not 

 know that their work is yet published in full. L. Horner 2 

 gives a capital balance of difficulties on the Coal-theory in 

 his last Anniversary Address, which, if you have not read, 

 will, I think, interest you. In a paper just read an author 3 

 throws out the idea that the Sigillaria was an aquatic plant 4 

 -I suppose a Cycad-Conifer with the habits of the man- 

 grove. From simple geological reasoning I have for some 

 time been led to suspect that the great (and great and 

 difficult it is) problem of the Coal would be solved on the 

 theory of the upright plants having been aquatic. But even 

 on such, I presume improbable notion, there are, as it strikes 

 me, immense difficulties, and none greater than the width 

 of the coal-fields. On what kind of coast or land could the 

 plants have lived ? It is a grand problem, and I trust you will 

 grapple with it. I shall like much to have some discussion 

 with you. When will you come here again ? I am very sorry 

 to infer from your letter that your sister has been ill. 



1 On the Physical Structure of the Appalachian CJiain, by W. B. and 

 H. D. Rogers. Boston, 1843. See also Geology of Pennsylvania, by 

 H. D. Rogers. 4 vols. London and Philadelphia, 1843. 



2 Quart. Journ. Geol Soc., Vol. II., 1846, p. 170. 



3 "On the Remarkable Fossil Trees lately discovered near St. Helen's." 

 By E. W. Binney. Phil. Mag., Vol. XXIV., p. 165, 1844. On p. 173 

 the author writes : " The Stigmaria or Sigillaria, whichever name is to 

 be retained .... was a tree that undoubtedly grew in water." 



4 See Life and Letters, I., pp. 356 et seq. 



