160 STEVENSON— FORMATION OF COAL BEDS. [April i8, 



formed, lie alongside of the flattened stems. Erect stumps are of 

 comparatively rare occurrence in the coal, but they abound in Ter- 

 tiary and Quaternary deposits. Evidently, cellulose predominated in 

 the older forms as lignin or woody tissue predominates in the newer. 

 As Andersson^^" says, if the cell walls of all plants had consisted of 

 pure cellulose, we probably should have found scarcely a trace of 

 the plant world which once existed upon the earth. 



Peat is laminated but not in all cases like coal, for in the latter, 

 the lamination is due very often to flattened stems. The existence 

 of well-preserved woody stems in many swamps obscures the lamina- 

 tion. But Lesquereux long ago recognized the layer-like structure 

 of new peat, where the thickness of layers is not far from an inch, 

 while in the mature peat it is not more than an eighth. Von Giimbel 

 ascertained that compression makes the lamination of even sphag- 

 num peat distinct. 



Peat beds have definite benches like coal beds. Lesquereux says 

 that in some bogs the ash is different in color. Such benches are as 

 well marked in peat deposits of northern Europe as in any coal bed 

 and they are equally well marked in the Schieferkohle of Switzer- 

 land, so that the history of each bench is clear. The passage from 

 one to another is abrupt, as appears from sections given in Part II. 

 There are, very often, distinct partings, consisting of a crust formed 

 during periods of dryness, when growth of peat is checked and 

 oxidation succeeds ; this crust persists after growth has been re- 

 sumed. Its character is very similar to that of the thin partings in 

 the Pittsburgh coal bed, which consist of mineral charcoal with 

 mostly impalpable inorganic matter, such as would remain after oxi- 

 dation of vegetable substance. Explanation of those partings in 

 this way seems to very simple and not far-fetched ; lowering of the 

 water-level only a few inches would suffice. The period during 

 which that bed accumulated was one of irregular and more or less 

 differential subsidence. 



On a preceding page, it was shown that the ash in coal is from less 

 than I per cent, to any per cent., the passage from coal to carbona- 



^" G. Andersson, "Studier ofver Finlands Torfmossar och fossila Kvar- 

 tarflora," Bull. Coin. Gcol. de Finlande, No. 8, 1898, p. 191. 



