66 STEVENSON— INTERRELATIONS OF THE FOSSIL FUELS. 



Preservation of Vegetable Ulatter in Bogs. — The chemical proc- 

 esses leading to conversion of plant matter into peat do not fall 

 within the scope of the present inquiry, but some features must be 

 considered, though without reference to their causes. 



Even a casual examination is enough to convince the observer 

 that these processes do not attack all plants or all portions of a plant 

 ec[ually. Bunbury^^ says that the peat in a great bog was found to 

 be merely a black mud, so decomposed as to show no vegetable struc- 

 ture; but at 15 feet down in this mud there was found a horizontal 

 layer, 2 to 6 inches thick, of compressed, undecayed moss, Hypniim 

 fliiitaiis, without admixture of other material. The peat below this 

 layer is like that above it. Skertchly"" notes a similar case. In the 

 turbary near Ely, the peat is digged to a depth of 4 feet. At the 

 top for about a foot it is chestnut brown and not bedded ; this is suc- 

 ceeded by 3 feet of black peat, which is bedded, contains roots of 

 reeds, flags, etc., but in the mass shows vegetable structure obscurely ; 

 at the bottom is a layer, almost wholly Hypmim, which dries to a 

 yellow tint and preserves the vegetable structure. It is well known 

 that the soft parts of plants disappear quickly to become the pulp, 

 in which the harder parts are embedded and of which they them- 

 selves eventually become part. 



The bark of trees is resistant, even that of trees whose wood 

 decays rapidly. Darwin''^ remarks that in the valleys of Tierra del 

 Fuego, it was scarcely possible to crawl along, the way being bar- 

 ricaded by great mouldering trunks, which had fallen in every direc- 

 tion. When passing over these natural bridges, one's course was 

 often arrested by sinking knee-deep into the rotten wood; at other 

 times, when attempting to lean against a firm tree, one was startled 

 by finding a mass of decayed matter, ready to fall at the slightest 

 touch. There are few living in the temperate zone who have not 

 been startled in like manner by the crashing of a log on which they 

 had set themselves in the woods. The bark had remained sound 



s^ C. J. F. Bunbury, " Notice of Some Appearances Observed in Drain- 

 ing a Mere," Quart. Jonrn. Gcol. Soc, Vol. 12, 1856, pp. 355, 356. 



^•^ S. B. J. Skertchly, " Geology of the Fenland." p. 135. 



•'i C. Darwin, " Journal of Researches," Amer. ed., New York, 1846, Vol. 

 I., p. 302; Vol. II., p. 44. 



