1892.] NATURAL SCIENCES OF PHILADELPHIA. 87 



theless by comparing the best verified of these, with personal obser- 

 vation and the result of individual inquiries, one may venture upon 

 an approximation subject to correction as time goes on and precise 

 information becomes more abundant and available. If the jDroblem 

 were presented to practical American geologists, supposing the 

 valuable coal remaining in all workable seams weie distributed in 

 a single bed of uniform thickness extending over the entire area, 

 not of coal, but of the carboniferous measures, assumed at 219,080 

 square miles, what thickness should be assigned to it ?, their reply 

 must, as has been seen, be largely hypothetical. Yet being based 

 on the several sources of information above referred to, it would 

 possess value as the opinion of a large body of close and intelligent 

 observers who have given careful observation and study to the sub- 

 ject as the most interesting of their lives. 



It is the belief of the present writer that the majority of such 

 observers would assign a thickness considerably less than six feet. 

 But assuming six feet to be an admissible working estimate, and 

 assuming the received quantity of 800 tons of 2240 lbs. each, 

 (about 42 per cent.), as that which is on the average mineable per 

 level acre per foot of thickness, we should then by a simple 

 arithmetical process get the following, viz : 219,080 square miles 

 equal to 140,211,200 acres, multiplied by 6 feet (of thickness) and 

 by 800, being the available tonnage, per foot of thickness from each 

 acre, would give the tonnage, which is 673,013 millions of tons. 



The same Census report states the production (and therefore the 

 consumption) during the year 1889, at 141,229,513 short tons of 

 2000 lbs. each, which is equivalent to 126,097,779 long tons of 2240 

 lbs. each, and further states the increase of consumption to have 

 been at the rate of 97.57, or in round numbers 100 per cent, per 

 decade. 



This rate of known actual increase applied to the present annual 

 consumption for thirty years, then reduced to fifty per cent, per 

 decade for the next forty years, and further reduced to thirty-three 

 and a third per cent, per decade for another forty-two years, would 

 indicate the entire consumption of every accessible ton at the end 

 of 112 years from the year reported on, or say by A. D. 2001. 



Of course the above is a broad generalization of results which 

 will probably be reached about the same time but in a different 

 manner. It is probable the rate of annual increase of consumption 

 would during the first half of the period show a much more rapid 



