ON THE ORIGIN OF COAL. 155 



generally termed, the carboniferous limestone, 

 may be considered as the base of the profitable 

 Coal-fields of the north of England. Professor 

 Phillips in his treatise on the deposit in Yorkshire, 

 divides it into two parts, namely, the lower lime- 

 stones and shales, and the Yoredale rocks or 

 limestone shale. Each of these divisions at the 

 greatest points of development reaching to near 

 one thousand feet. The thickness of the lower 

 limestone in Flintshire, I have not been able to 

 ascertain, but the limestone shale in that county 

 does not appear (if at all) to anything like the 

 extent which we find it in Yorkshire and Derby- 

 shire. The organic remains in both deposits, 

 consisting of corals and shells, lead us to suppose 

 that the creatures which belonged to them lived 

 in seas of moderate depth ; and that the beds of 

 those seas were gradually subsiding, so as to 

 compensate for their filling up by the deposition 

 of carbonate of lime, sands, and argillaceous beds, 

 brought thither by the water. 



Having thus hastily glanced at the deposits on 

 the crust of the globe, which were found prior to 

 the millstone grit, and shown the evidences of 

 continued subsidence in some portions of it com- 

 pensated for, by continuous sedimentary deposits, 



