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



Appalachian basin. The thickness of certain coal beds has been 

 regarded as weighing heavily against autochthony. But the modern 

 peat bogs, which have been studied in detail, are youthful, of only 

 post-glacial origin. Possibly in course of time there may be at 

 many places peat deposits of immense thickness like those in some 

 portions of the Alaska tundra ; but it is more probable that no 

 deposit will excel the average coal bed ; reclamation of marsh land 

 has checked peat accumulation in much of Germany and is likely to 

 do it throughout the civilized world. 



The earlier writers studied mostly the treeless moors ; but many 

 features of coal beds, wanting in those, are reproduced in the Wald- 

 moors or forested swamps, which are familiar in much of northern 

 Europe and in the United States. In all probability they are of 

 much greater extent on the broad plains of the Amazon and Ori- 

 noco, where, however, they have been studied only as forested 

 swamps and not as producers of peat. Kuntze has shown that 

 similar areas of vast extent in the Paraguayan region are genuine 

 ^^"aldmoors. The prevailing flora of such swamps in the tem- 

 perates consists of conifers, heathers, sedges, with ferns and, usually 

 as late arrivals certain mosses. These plants are in a habitat resem- 

 bling that in which the Coal ]\Ieasures plants are supposed to have 

 lived, so that there should be important features in common, if the 

 doctrine of autochthonous origin be true — for that asserts that the 

 older flora grew in areas covered with decomposing vegetable 

 materials. 



The swamp flora of modern times consists very largely of plants 

 with marked xerophytic or drought-resisting features ; similar char- 

 acteristics have been recognized in the Coal Measures flora, as well 

 as in those of some later coal-making times. The facts that some 

 plants living in swamps are found elsewhere, flourishing on arid or 

 semi-arid soils, has led to the suggestion that they may be only inter- 

 lopers. Henslow^^° has conceived that the xerophytic features of 

 Stigmaria and Lepidodendron could have been acquired by living 



^^^ G. Henslow, " On the Xerophytic Characters of Certain Coal Plants, 

 and a Suggested Origin of Coal Beds," Quart. Jourii. Geol. Soc, Vol. LXIIL, 

 1907, p. 283. 



