coal-fields of the country, where the bulk of the best coal-lands has been let and occupied, are, as compared with the newer developed coal-fields, already showing a retarded rate of increase of output. And as the Midlands and South Wales unoccupied coal-lands become acquired for working, the rate of increase must gradually lessen, and in time the working of thinner seams will further reduce the butput capacity of the collieries, so that the writer is of opinion that it may be assumed that the operation will probably be as follows: a continued gradually increasing annual output of coal in the country, with a rate of increase that is itself gradually decreasing, until nearly the whole of the coal-lands are let and occupied, followed by a more or less stationary condition for a considerable period, to be followed as the thick and easily worked coal is exhausted by a gradually diminishing annual output. If this indication of the probable course of events is approximately correct, the estimate of the Royal Commission of 1871, of the total coal res. ources existing at that period of 140,000 million tons (allowing a wide margin for that statement being possibly a considerable over-estimate of the actual workable resources), still leaves an ample supply to meet the country's requirements for several centuries, and therefore the actual exhaustion of our coal supplies is neither imminent, nor a matter for immediate consideration; but the immediate pertinent inquiry is, how long will what may be described as the cream of our coal resources--namely, the thickest and most cheaply worked seams existing at a moderate depth below the surface last: and what will be the effect of the subsequent increased expense of working upon the national finances and income ?
When the depth below the surface exceeds 2,000 feet, or the thickness of a seam becomes much less than 3 feet of clean coal, or even a greater thickness of coal where bands of stone intervene, it may be assumed that the cost of working becomes greater where compared with a shallower depth below the surface than 2,000 feet; or thicker seams than 3 feet of clean coal. We have, unfortunately however, no information which would be a reliable guide, by which to estimate the proportion which the thickest and best of our coal-seams in the principal coal-fields existing at a less depth than 2,000 feet below the surface, originally bore to the total coal resources.
To begin with, the minor coal-fields, as not affecting the question of our commercial status materially one way or the other, may be excluded from consideration, and the estimate may be fairly narrowed to the proportion of the best coal originally
