450 STEVENSON— INTERRELATIONS OF FOSSIL FUELS. 



formed partings, to be covered in succeeding time of quiet by a new 

 deposit of plant stuff. 



Periodically, perhaps because of crustal movements, notable 

 changes came about in the fall of streams, leading to violent flood- 

 ings. Then rock materials predominated and deposits of sand, mud 

 and pebbles were formed, covering the plant materials, which are 

 now the coal beds. Later came the period of quiet and the Wald- 

 moor expanded to its former luxuriance. During the interval, many 

 species of plants had been destroyed while others survived and new 

 forms appeared. This doctrine of local change does not exclude 

 changes in the lake bottom ; that might be brought to a higher level, 

 so that growth of plants might begin on it. Increased accumulation 

 of detrital material in the lake would have the same effect. Per- 

 haps, in some places of this sort, there grew the vertical stems, 

 giving a local autochthonous formation. 



Sterzel's conception closely resembles that presented by Grand- 

 'Eury in 1882, which was abandoned by that observer after his 

 knowledge had been increased by careful studies in regions aside 

 from his own basin of St. Etienne. But the presentation is far from 

 being conclusive. 



Lamination of coal is by no means evidence that the material 

 was transported; autochthonous peat, subjected to pressure, has the 

 same structure. Sigillaria and Lepidodendron occur in roofs of 

 coal seams ; as Stigmaria is the rhizome of those plants, it ought to 

 occur in roofs. Partings, such as those of coal seams, are familiar 

 features of autochthonous peat deposits. Vertical stems are appar- 

 ently rare and local in roofs, but there are vast areas of growing 

 peat without trees, while there are other areas in which the Wald- 

 moor condition prevails. It must not be forgotten that our knowl- 

 edge of roofs is confined chiefly to exposures in mines, where the 

 stems are only too abundant. 



There is not much basis for the suggestion that a great lowland 

 area, covered with Waldmoor, was the region surrounding the 

 Zwickau lake. The Erzgebirge had been elevated prior to Carbon- 

 iferous time and the Zwickau basin is at the foot of those mountains. 

 Even if there had been a great Waldmoor area, it is inconceivable 

 that streams meandering across it could bring down such great quan- 



