existing in the Scottish, Durham, Northumberland, Lancashire, Midlands, including Staffordshire, and South Wales coal-fields.
In many parts of these coal-fields the best and thicker seams do not amount to more than from 6 feet to 20 feet in total aggregate thickness. Now our annual output is equal to the exhaustion of a coal-seam 6 feet in thickness extending over 30,000 acres, but, dealing with the question very broadly, the writer is disposed to estimate the total original resources of our best and cheapest seams, upon the working of which our commercial position has hitherto depended, at approximately twenty thousand million tons. Of this quantity it may be further estimated that about one- fifth has been already worked. The duration of what remains is of course contingent upon the future rate of output, and upon this point there exists room for a wide diversity of opinion. It appears to have been assumed by several writers that our output of coal would continue to increase at possibly a somewhat decreasing rate, until the cost of working becomes so excessive as to permanently check the progress of the coal industry, and that our annual output of coal, having regard to the total coal resources of the country, may probably reach an enormous figure. As has been already hinted, the writer holds this view only in a modified degree.
The continuous and rapid development of our coal-fields during the past forty years, has been due partially to causes which will not continue to operate for any long period in the future.
The enormous trade development which followed the discovery of the use of steam as applied to industrial purposes, associated with our comparatively virgin coal-fields, led to an exceptionally rapid development of our coal resources. That cause still continues to operate, but in a modified form, and probably sufficient consideration has not been given to the retarding effect of the occupation of the available surface of the coal area by collieries. In addition to this, upon the complete occupation or letting of the available area of coal, the area may be broken up into very lrge blocks for working purposes, containing from 20,000 to 40,000 tons per acre, and of from 1,000 to 3,000 acres in extent, and under such circumstances, although the actual coal resources may be very large, yet the power of increasing the output so occupied, will be very much restricted, because fewer new pits will be sunk than is practicable where a virgin coal-field exists unoccupied. Hence the annual increase in the development stages of the coal output of this country may therefore be very rapid,
