134 LIFE ON THE EARTH. 



the total thickness of Coal, some beds being Anthra- 

 citic and some ordinary Coal, is 120 feet. To produce 

 this thickness of ordinary Coal, by vegetables growing 

 on the spot, would require 120 x 12 x 127'5 = 183,600 

 years. The same thickness of Anthracitic Coal would 

 require 120x12x170 = 244,800 years. Add to either 

 of these periods the lowest number of years found 

 for the deposition of the sediments in the same 

 coal-field, 333,000, and we have as the probable 

 length of time required for the production of the 

 Strata of Coal, Sandstone, Shale, and Ironstone in 

 South Wales, half a million of years. 



If now we turn to the Leibnitzian Theory, and 

 apply it to the same problems, we must first settle 

 the limits of the atmospheric power to waste the 

 surface in the early geological periods. This limit 

 at the origin of the oceans needs not to be inquired 

 into ; there would indeed be a mighty power in ac- 

 tion perpetually falling floods the fountains of 

 heaven wasting a hot and friable surface 1 . Coming 

 down to the base of the Palaeozoic System, and 

 adopting as high a limit for the temperature of the 

 surface of the globe as might be possible to suit 

 the races of Mollusca and Crustacea then coming 

 into view, we may allow 20 higher mean tempera- 

 ture than at present. From this point it must be 

 1 Babbage. Ninth Bridgewater Treatise. 



