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



channel. This hypothesis explains local abundance of fragments by 

 two factors; their previous existence in the mur and the fragility of 

 the mur itself; so that they would form in succession part of the 

 mur and part of the coal. The purity of the coal eliminates, during 

 formation of the bed, the agency of convoys of allochthonous trees 

 loaded with extraneous debris. 



The condition is not peculiar to the Coal Measures. It is found 

 in coal formations of other ages. Hutton^^ found in the Upper 

 Cretaceous of southern New Zealand a sandstone mass, 8 feet by 3, 

 resting on the coal, which convinced him " that there can be no doubt 

 that this boulder has been floated to its present position among the 

 roots of a tree and that therefore the coal beds are formed partly 

 from driftwood." He states the Tertiary brown coals in several 

 fields contain pebbles of white quartz ; these beds, according to 

 Hector, rest on fireclay. Jack®*' found pebbles in coals of Upper 

 Cretaceous age in Queensland. 



The presence of rock fragments in coal has always been per- 

 plexing to allochthonists and autochthonists alike, though each seems 

 to be certain that in some way or another they afford an important 

 argument in favor of his doctrine. They are certainly transported 

 materials ; some were brought from rocks far away and most of 

 them are distinctly waterworn. H all were small, any geologist 

 could conceive of an explanation, which would be satisfactory to 

 himself, as refutation might be difficult; but when one has to deal 

 with masses of several hundred pounds, such as the Ohio blocks, 

 transported several hundreds of miles, the problem becomes serious. 



Some writers have been inclined to regard ice as the transporting 

 agent; but the character of the Coal Measures vegetation appears to 

 be conclusive against the supposition that intense cold prevailed dur- 

 ing any part of the year at any locality whence the fragments have 

 been reported. It is very true that sharply contrasted climates may 

 exist only a few miles apart, as in southern California, but that 



*" F. Hutton, '' Report on Geology and Gold Fields of Otago," Dunedin, 

 187s, pp. loi, 103. 



*'R. L. Jack, "Geology and Palaeontology of Queensland and New 

 ■Guinea," London, 1892, pp. 536, 538. 



