604 GEOLOGY 



formably on the Devonian in many parts of Europe, they never- 

 theless record considerable geographic changes, for the early Car- 

 boniferous formations of western Europe are of marine origin, 

 while much of the underlying Devonian (the Old Red Sandstone) 

 is not. The distribution of the two systems and the character of 

 their formations, indicate a somewhat wide-spread, even if slight, 

 submergence at the opening of the early Carboniferous period. 

 This is in keeping with the course of events in North America. 



The Lower Carboniferous system of western Europe, like that 

 of North America, is largely of limestone, sometimes known as the 

 Carboniferous Limestone. In Great Britain, the system early 

 received the name of "mountain limestone," and this name has 

 been applied frequently in North America. East of the Rhine 

 the Lower Carboniferous limestone is replaced by shale, sandstone, 

 and even conglomerate, collectively known as the Culm. This 

 phase of the system contains coal in some places. 



In eastern Europe, the system contains much coal. The coal- 

 field of Moscow covers 13,000 square miles, but the beds of coal 

 are mostly thin and poor. The coal-field of Donetz covers 11,000 

 square miles, and contains 44 workable beds (some of them Upper 

 Carboniferous) which have an aggregate thickness of 114 feet. 

 Workable coal beds also occur in the upturned Lower Carboniferous 

 strata on the flanks of the Urals. 



The Lower Carboniferous of some parts of Great Britain and 

 western Europe contains much volcanic rock. Some of the erup- 

 tions were probably submarine, and some subaerial in origin. 



Thickness. The thickness of the European Lower Carboniferous 

 is very great, considering the fact that it is so largely of limestone. 

 In England and Ireland, the limestone attains thicknesses ranging 

 up to 2,000 feet, and perhaps even to 2,500 feet. In the northern 

 part of England and in Scotland, where the beds are clastic, they 

 have a thickness which, at the maximum, is much greater. In 

 Belgium, also, the limestone is very thick, bespeaking the great 

 duration of the period. At the rate at which limestone is supposed 

 to accumulate, 2,500 feet of limestone would call for at least some 

 hundreds of thousands of years. 



The close of the early Carboniferous period was marked, in 



