46 Editorial Comment. 
ns only 8,786,858,666 tons to send to market. In all our calculations of 
anthracite we have counted the area as if in a level plain, and made no 
allowance for the undulations which must necessarily increase the amount 
of coal. But as many of the flexures are abrupt and broken, making 
much faulty and refuse coal, it will cover any over-estimate of area or of 
thickness we have made in our calculations. Our tables show that 360,- 
017,817 tons have been sent to market in tlie 59 years from 1820 to 1878 
inclusive. Our consumption now amounts to 20,000,000 tons annually. 
The increase of production for the past ten years has been 187,113,857 
tons. At this rate we shall reach our probable maximum output of 50,- 
000,000 tons in the year 1900, and will finally exhaust the supply in 186 
years. 
Recent re-estimates made by the editor of the Mining and 
Engineering Journal vary considerably from these results. 
These estimates fix the amount of coal in the ground as 9,000,- 
000,000 tons, two-thirds of which is waste, leaving 3,000,000,- 
000 tons as the total amount of available coal to be mined. 
With the present lavish methods of mining, and with the pre- 
sent increasing amount of coal marketed, this would be exhaust- 
ed in seventy-live years. This causes Mr. Sheafer to reconsider 
his former calculation and he comes to the conclusion that the 
time he formerly allowed for the exhaustion of the anthracite 
coal deposits v/as too great, and that the aunual output is in- 
creasing at a rate hardly expected by any statistician ten years 
ago. He distributes the present available tonnage as follows: 
Tons. Tons. 
1st. Southern field 4.000,000,000 Workable ('J 1,833,010,000 
2nd. Middle field 1,800,000,000 " 600,000,000 
3d. Northern field 3,200,000,000 " 1,066,000,000 
The present rate of shipment is: 
First field, percenta shipment, 30 percent 12,000,000 
Second field " 18 " •' 7,200,o00 
Third field, " .52 " " 20,800,000 
100 -10,000,000 
At these ratios of shipment, the Wyoming region would exhaust itself in 
51 years, leaving the other regions to supply tlie demand with workable 
coal after that time. 
Tons. 
Southern field 721.000,000 
Middle field 232,800,000 
Assuming each field to double its proportion and ship as follows: 
Southern field, 65 per cent, Middle field, 35 per cent, in 16% years more, 
or 67 % years hence, the Middle field would be totally exhausted, leaving 
the Southern field with less than 300,000,000 tons of coal to mine, that 
would last 71^ years longer, or a total exhaustion in 75 years. 
Mr. Sheafer calls attention to some improved methods of 
