192 ON THE ORIGIN OF COAL. 



bedded in it ; but the under portion of it, nine 

 inches in thickness, is a rich iron ore. The whole 

 mass of the Bass and ironstone, like the Bass above 

 the yard Coal, teems with remains of Cypris and 

 Microconchus, detached bones, scales, and teeth 

 of fishes of the genera Megalichthys, Holop- 

 tychius, Cselacanthus, Platysomus, Palseoniscus, 

 Diplopterus, Ctenoptychius, and shells of the 

 genera Unio and Modiola, all mingled together. 



The three sections of strata containing fossil 

 trees, heretofore referred to, may also be brought 

 as proofs to show the change of level and con- 

 dition of the earth's surface, at the period of 

 their formation ; but their changes in structure, 

 especially those of the two last, are so regular 

 and slow, as to show but little variation in the 

 rate of subsidence. The St. Helen's section 

 commences with a mass of vegetation now forming 

 the foot coal, grown during a period of repose 

 of the area on which it is found. It then subsided, 

 at first slowly, but gradually increasing. The sub- 

 sidence was at length rapid enough to prevent the 

 growth of plants, so long as the White Sandstone 

 Rock was in the process of formation. When 

 this was done, however, it became gradually slower, 

 so as to allow of the formation of the Warren, and 

 the growth of the Sigillarise found in it. 



