STEVENSON— INTERRELATIONS OF THE FOSSIL FUELS. 57 



though the wood was wasting away. The rate of decay is indefinite. 

 Darwin estimated that in the neighborhood of Valdivia in ChiH, a 

 stump of 1 8 inches diameter would be changed into a heap of mould 

 within 30 years ; but in Java, Koorders, cited by Potonie, saw much 

 fallen timber, decades old yet still in condition for export. In the 

 northern part of the United States, stumps of maples, elms and 

 spruces, 18 inches to 2 feet or more in diameter, are often sound 

 enough after 25 years of exposure to require blasting for their 

 removal. The wood of oaks and conifers is especially resistant, yet 

 even those may go rapidly. Lesquereux,^- in referring to the sunken 

 forest of Drummond lake in the Dismal Swamp, says that standing 

 stumps of bald cypress (Taxodimn distichuni) are decaying so that 

 many of them are hollow. Fruits and leaves of trees, falling into 

 the water and drifting, are arrested by the hollows of these trees 

 and fill them almost completely. De la Beche,*'^ in discussing the 

 decay of plants, observes that " this kind of decay is still more in- 

 structive where upright stems of plants in tropical low grounds, 

 liable to floods, retain their outside portions sufficiently long to have 

 their inside hollows partially or wholly filled with leaves and mud or 

 sand, the whole low ground silting up, so that sands, silt and mud 

 accumulate around these stems, entombing them in upright position, 

 without tops, though their roots retain their original extension." 

 Potonie, in 1895, called attention to the fact that hollow alder stumps 

 in West Prussia swamps, exposed to high water, are filled with sand 

 even to the roots, so that they must be cleaned out before the axe is 

 applied. 



Generally speaking, the wood of deciduous trees decays rapidly 

 while that of conifers changes slowly. Lesquereux, on the page pre- 

 ceding that just cited, records that in Denmark, about 20 miles below 

 Copenhagen, there is an extensive grassy plain with one foot of 

 humus as the soil. Underlying that is a bed of peat-like material, 

 6 feet thick, composed wholly of closely packed, flattened birch bark. 

 This, free from earthy matter, is cut out and dried in long rolls. 

 The woody part of the stems, now nearly fluid or transformed into 

 a very soft yellow mud, is at the bottom of the deposit, whence it is 



'^~ L. Lesquereux, " Geology of Pennsylvania," 1858, p. 847. 

 '^^ H. T. de la Beche, " Geological Observer," p. 133. 



