86 STEVENSON— FORMATION OF COAL BEDS. [April 21. 



contact. The thickness and extent of some coal deposits are serious 

 objections to growth in situ. Richthofen describes a bed in China, 

 20 to 30 feet thick and having an area of 600 German square miles. 

 This would require at least 400 feet of plant remains. The bottom 

 three feet might have been a soil in which Stig}iiai'ia rhizomas could 

 have grown, but the sturdiest defender of autochthony would be at 

 loss to find a soil for the remaining 397 feet. Such a deposit could 

 have been made only by a matt of sylvo-marine vegetation. 



All allochthonous and land basin theories are untenable because 

 transportation yields no undisturbed sedimentation ; there is no 

 transportation of organic detritus without contemporaneous trans- 

 portation of inorganic material — the transportation of purely plant 

 detritus is a superstition ; subsiding land basins giving 7,000 me- 

 ters of Carboniferous rocks, while neighboring basins subside at 

 different rates, would be a marvel, for in order to account for 

 the thick mineral beds the process of coal making would have to 

 be intermitted a hundred times ; there are no basins so great as those 

 of coal sedimentation. The four great deltas do not equal the 

 Pennsylvania coal-field alone ; Richthofen's southeast Shansi field 

 would require a basin sixteen times as large as the Caspian sea. 

 The great basins must have been sea basins and a sylvo-marine 

 forest alone explains the intermittent deposit of coal, the clays being 

 due to influence of streams. 



Kuntze classifies the theories as Autochthony, the irregular de- 

 posit of the coal-producing substance directly on the place of vegeta- 

 tion ; Allochthony, the irregular deposit of coarse coal-producing 

 substance on a distant place ; onl}- the powdery substance is depos- 

 ited after the manner of sediments. 



Pelagochthony, the sedimentary deposit of coarse substance in 

 water of the sea directly under the vegetation ; a secondary product 

 is the powdery detritus sometimes floated away from the coal magma 

 and deposited elsewhere as anthracite. 



Autochthonous types are found in tropical or subtropical brown 

 coal from wood-covered bogs, witlujut s])hagnum; newer peats in 

 cooler regions with sphagnum ; shore swamps and some others. 



Allochthonous types are drift woods; sedimentary peats; sea 



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