THE CARBONyEEODS AGE. 113 



Roderick Murchison tells us of 10_,000 feet in thick- 

 ness of red iron-stainod rocks in the old red sand- 

 stone of England, we can see in this the evidence of 

 rapid aqueous deposition, going on for a very long 

 time, and baring vast areas of former land surface. 

 Consequently we have proof of changes of level and 

 immense and rapid denudation — a conclusion further 

 confirmed by the apparent unconformity of different 

 members of the series to each other in some parts of 

 the British Islands, the lower beds having been tilted 

 up before the newer were deposited. Such was the 

 state of affairs very generally at the close of the 

 Devonian, and it appears to have been accompanied 

 with some degree of subsidence of the land, succeeded 

 by re-elevation at the beginning of the Carboniferous, 

 when many and perhaps large islands and chains of 

 islands were raised out of the sea, along whose mar- 

 gins there were extensive volcanic eruptions, evi- 

 denced by the dykes of trap traversing the Devonian, 

 and the beds of old lava interstratified in the lower 

 part of the Carboniferous, where also the occurrence 

 of thick beds of conglomerate or pebble-rock indicates 

 the tempestuous action of the sea. 



But a careful study of the Lower Carboniferous 

 beds, where their margins rest upon the islands of 

 older rocks, shows great varieties in these old shores. 

 In some places there were shingly beaches ; in others, 

 extensive sand-banks ; in others, swampy flats clothed 

 with vegetation, and sometimes bearing peaty beds, 

 still preserved as small seams of coal. The bays and 



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