416 THE CARBONIFEROUS PERIOD 



Thus, in Carboniferous times we observe a striking difference 

 between the development of the eastern and western halves of 

 the continent. At first, there was a deepening and extensive 

 transgression of the sea. This was followed in the eastern interior 

 region by the upheaval of vast areas into low, swampy flats. In the 

 West the sea held sway throughout the period, and the conditions 

 for the accumulation of coal were not brought about. This was 

 done, as we shall learn, at a far later time. In the East there 

 were numerous oscillations of level, as is shown by the character 

 of the strata, though the movements were very slow and gentle ; 

 but in parts of the West, as around the Colorado island, there 

 were some disturbances, and unconformities between the Upper 

 and Lower Carboniferous beds have been detected. No volcanic 

 rocks have been found in this system, East or West. 



Foreign. — In Europe the Carboniferous system is developed 

 in a very interesting way. In the western and central parts of 

 the continent (and in Great Britain) the succession of strata is 

 very similar to that of the eastern half of North America, while 

 in Russia it has more analogy with the western half of our 

 continent. The changes of level which opened the period con- 

 verted much of the Devonian sea-bed into land, but at the same 

 time the sea broke in over many of the closed basins in which 

 the Old Red Sandstone had been laid down. From the west of 

 Ireland to central Germany, a distance of 750 miles, stretched a 

 clear sea, free from terrigenous sediments, in which flourished an 

 incredible number of corals, crinoids, and other calcareous organ- 

 isms. From their remains was constructed an immense mass of 

 limestone, having a thickness of 6000 feet in the northwest of 

 England and of 2500 feet in Belgium. Above this great "moun- 

 tain limestone," as it is called in England, come the coal meas- 

 ures. In Scotland the limestone is replaced by shore and shallow- 

 water formations, such as sandstones, with some coal. In the 

 southwest of England and east of the Rhine in Germany, the 

 Lower Carboniferous is represented, not by a limestone, but by a 

 series of sandstones and slates, called the Culm, with the coal 

 measures above. In Russia the order of succession is reversed, 



