THE PENNSYLVANIAN PERIOD. 585 



of 5500 feet. 1 This formation has the same stratigraphical position, 

 and probably the same significance as the formation of corresponding 

 name (Pottsville, etc., see p. 539) in America. 2 It was indeed this 

 correspondence which led to the adoption of the English name for 

 the American formation. The thick Millstone grit of England is 

 thought to represent a shore accumulation against a ridge of Paleozoic 

 rock which crossed central England in the early part of the Carbon- 

 iferous period. The ridge was later submerged, but not until some part 

 of the Coal Measures had been deposited. North from this ridge the 

 Millstone grit thins rapidly. The fossils of the Millstone grit are 

 singular in that the plants resemble those of the Coal Measures above, 

 while the animals are more like those of the Lower Carboniferous 

 below. 3 



The formations of the western European Coal Measures, like those 

 of eastern North America, consist principally of shales (and clays), 

 with subordinate amounts of sandstone and limestone. Associated 

 with these commoner sorts of rock, there are beds of coal and clay- 

 ironstone, both of which occupy positions corresponding in all essen- 

 tial respects, with those of the similar formations in eastern North 

 America. As in America, there are local unconformities within the 

 system. The system contains workable coal in Great Britain, Ireland, 

 Belgium, France, Spain, Germany, Austria, and Russia, but the total 

 area of productive coal in Europe is much less than in America. In 

 places in Wales, there are as many as 100 seams of coal, many of which 

 are worked. In Belgium, and in some parts of Germany the number 

 of coal-beds is also very large. In Westphalia the number of workable 

 beds is said to be 90. 4 The aggregate (maximum) thickness of the 

 coal in Lancashire is 150 feet; in Westphalia, 274 feet; in Mons 

 (Belgium), 250 feet. In central and northern France there are more 

 than 300 small areas where portions of the Coal Measures are found. 

 Some of them contain remarkable thicknesses of coal. 5 The Coal 

 Measures of central Europe are less wide-spread than the Lower Car- 

 boniferous in the same region. Coal-beds are numerous in the Coal 



1 Geikie, Text-book of Geology, Vol. II, p. 1047. 



2 The Millstone grit is sometimes regarded as the representative of a separate time- 

 division coordinate with the Lower and Upper Carboniferous. 



3 Geikie, p. 1054. 



4 Idem, p. 1047. 



5 Idem, p. 1053. 



