184 ON THE ORIGIN OF COAL. 



the deposition of our Coal seams. Every seam 

 of Coal indicating a period of rest of the earth's 

 crust, which allowed the growth of a forest of 

 trees ; whilst the sandstones, shales and binds, 

 give us a correct measure of the rate of subsi- 

 dence, and the force of the currents caused by 

 such changes of the surface of the globe. As 

 before stated, there are, in the Lancashire Coal- 

 field, one hundred and twenty beds of Coal, which 

 would require as many epochs of rest, and the 

 same number of subsidences, to account for their 

 origin, a period of time, vast to our ideas, but 

 small in the history of the earth. 



In a former paper (p. 1*78, Vol. i. of the 

 Transactions of the Manchester Geological So- 

 ciety) I have stated, that the Coal measures 

 presented some appearance of having been depo- 

 sited in an estuary ; but further observations, and 

 the great superficial extent of the formation, now 

 lead me to believe that they must be considered 

 more of a marine character, and that the currents 

 which brought the debris^ did not altogether 

 proceed from rivers running into the sea, or by 

 tidal action, but were chiefly produced by the 

 subsidence of the bottom of the ocean itself. 

 The occurrence of the Cypris and the Unio, in 



