401 
eastern part of this county and the counties of Derby 
and Nottingham, the depth and consequent cost of winning 
is such that very large capital will be required. 
The quantity of coal annually worked in this country is 
upwards of eighty millions of tons, which requires annually 
the complete exhaustion of 16,000 acres, or 25 square miles 
of a bed of coal 50 inches in thickness. It must, therefore, 
be plain enough that the entire exhaustion of our coal-beds 
is but a question of time ; this depending on the quantity 
annually raised, the area of the coal containing strata, and 
the depth and thickness of the beds which can be worked to 
profit. Long before the beds are entirely exhausted, the 
thickest, most accessible, and most valuable beds now known 
will have ceased to exist for ever, and our future supply will 
be dependent on thinner and deeper beds. 
In this country, coal-beds vary from less than an inch in 
thickness, to upwards of 30 feet. [Much the greatest pro- 
portion of our present supply is from beds of from 3 to 6 
feet in thickness. After all such beds are exhausted, as much 
or more coal will remain in thinner beds as is found in what 
are now deemed beds of a workable thickness. 
A careful examination of the strata passed through in 
sinkings in different parts of England proves that upwards of 
60 per cent, of the coal contained in the coal-measures 
exists in beds under 3 feet in thickness. 
One of the greatest physical difficulties in deep mines is 
their high temperature. In mines 2,000 feet deep the 
temperature is frequently 90 degrees ; and it does not vary 
much between winter and summer, except at a very limited 
distance from the shafts. The temperature of the strata 
increases one degree for every 60 feet ; and if a depth of 
4,000 feet were reached, that being supposed to be possible, 
the temperature of the interior of the mine would be from 
100 to 120 degrees: the constitution of man, however, could 
LL 2 
