1892.] NATURAL SCIENCES OF PHILADELPHIA. 97 



consumption of coal, and the growth of population stimulated by its 

 use, it must soon be carefully sought for in every accessible quarter 

 of the world ; and it cannot be many years before such information 

 will be possessed as may enable us to dispense with most of the 

 hypotheses now required, and bring the entire subject of its quantity 

 and duration more or less within the limits of exact computation. 



The present object of this paper scarcely aims at more than the 

 hastening of such researches, and quickening the interest of more 

 ■competent analysts and naturalists. 



