I9II.] STEVENSON— FOR^IATIOX OF COAL BEDS. 49 



disappears, aside from soluble alkaline compounds. Some have 

 found proof of transport in the composition of ash from stone coal, 

 since it is quite similar to clay shale. But Mietzsch points out that 

 living Lycopodiacccc contain from 22 to 26 per cent, of clayey earth 

 in the ash and asks why one should suppose that the older types were 

 dififerent. But if the coal contain an abnormal proportion of ash, 

 there is reason to recognize influx of fine mud. 



The fineness of the materials, clay and sand, in contact with the 

 coal, proves a long period of quiet ; and the same may be said of 

 the plant deposits themselves. Such a period can hardly be ac- 

 cepted for rivers or for currents along coasts. The conditions of 

 the underclay ; the resemblance of the clay in many cases, as Stefifens 

 showed, to vegetable mould; the interlacing of Stigmaria roots like 

 wicker work; and the occurrence of erect trunks are all opposed 

 to the doctrine of transport. In most cases the conditions can be 

 explained only by the doctrine that coal beds owe their origin to 

 plants which grew where their remains are now found. He accepts 

 the peat bog theory as advanced by v. Beroldingen and presents 

 many facts as additional evidence in its support. The advance of 

 bogs into lakes is proved by the discovery of pile constructions in 

 Swiss peat bogs ; along the seashore, algae form dense floating felts 

 on which bog plants grow and the mass sinks to the bottom. Zee- 

 land was once cut by ba}s much longer than now and part of the 

 former sea-area is filled with peat. He strengthens his argument by 

 many references to phenomena observed in the great swamps of 

 Europe and North America. 



In order to explain the origin of coal-bearing strata, holding a 

 number of coal beds, one must distinguish between those formed 

 along a coast and those formed along rivers or in the interior of an 

 island or continent. Those of the first type are explained by the 

 subsidence of coasts bordering on the North Sea. The preliminary 

 work for drainage of the Zuyder Zee, as well as similar work else- 

 where, has proved the existence of peat bogs in extended areas of 

 shallow sea ; anchor flukes have brought up peat from depths of 200 

 meters on the English coast. Such bogs become covered by river 

 sediments and in case of long-continued slow sinking, the shallow 

 sea area is filled, so that a number of bogs may be formed suc- 



PROC. .-MVIER. PHIL. SOC, L, IQSD, PRINTED APRIL 24, IQII. 



49 



