STEVENSON— INTKRRKLATTONS OE THE EOSSIL EUELS. 199 



and that, in considerable spaces, the coal has been removed and has 

 been replaced with sandstone. 



The intimate resemblance of many brown coal deposits to those 

 of peat has been affirmed by many observers. Collier recognized the 

 resemblance in Alaska and Washington as did Eldridge in Alaska; 

 Haast was positive respecting it in southern New Zealand ; several 

 authors have described the Moor- and IMooskohle of Prussia and 

 Bohemia ; Gothan and Horich have shown that the Torfdolomite of 

 the Lower Rhine is merely mature peat replaced by inorganic matter ; 

 Smith and Travers-''^ described as peat an impure brown coal under- 

 lying the London clay. In many places the coal has been found rest- 

 ing on the characteristic reed beds. 



Few students have made minute investigation of the structure 

 and succssion of individual beds. Penck's observations at Tanndorf 

 have made clear that the brown coal at that place is in a lake basin : 

 the muddy floor afforded roothold for floating plants, on whose debris 

 rushes and other plants of similar habit grew, until the surface be- 

 came such as to permit growth of shrubs and trees. Others have 

 reported the occurrence of swamp plants in the brown coal, but they 

 have not said anything about their vertical distribution in the deposit. 

 Similarly, the presence of land and freshwater shells has been noted 

 by numerous writers, but there is rarely any information as to their 

 distribution in the bed. All that one may assert is that these indicate 

 the existence of pools or ponds in the marsh. Expansion of the 

 accumulating area by transgression, after the manner of swamps, is 

 distinct at many places. Stohr has shown that in a part of Prussian 

 Sachsen, the deposit began on an irregular surface as a number of 

 separate lenses, which often became united by crossing the dividing 

 ridges ; so that the coal is from o to 20 meters thick, being thinnest 

 on the low rolls separating the narrow troughs. D. White's descrip- 

 tion of conditions at Lehigh, North Dakota, is wholly similar ; the 

 greatest thickness is in the hollows of the floor and the coal becomes 

 thinner toward the "rise." At Senftenberg and Orebkau, as appears 

 from description by Potonie and Russwurm, transgression upon 

 forests is clear. At Senftenberg, the forest was living when the marsh 



^G-"' W. Smith and M. W. Travers, Journ. Soc. Chcm. hid., Vol. XL, 1892, 

 P- 591. 



