294 
POPULAR SCIENCE REVIEW. 
Many guesses have been made ; but although one may be 
a little more ingenious than the other, they must, every one 
of them, be received as guesses and nothing more. In con- 
sidering this important problem, several questions must receive 
the best possible answers which can be obtained. 
1. What is the area of the British coal-fields, within their 
known limits ? 
2. Can the quantities of coal which have been removed from 
the several fields be ascertained ? 
3. What is the total quantity of workable coal remaining in 
the collieries now at work ? 
4. What is the present rate of exhaustion ? 
5. What are the prospects, as it regards the annual increase 
of the “ output 33 (the quantity raised from each colliery) . 
6. Do any of our large coal-fields probably extend far 
beyond their known limits, under the Permian and New Red 
Sandstone rocks ? 
7. What seams of coal exist at greater depths than those 
now worked ? 
8. What are the difficulties in the way of carrying our 
mining operations to a depth much greater than the deepest 
workings now in progress ? 
With the three last questions I do not propose dealing, 
beyond the remark, that we know our coal-fields do extend under 
the Permian and New Red Sandstone rocks, and that coal 
seams do exist at much greater depths than any now worked. 
The extension of workings either horizontally or vertically 
will only take place as an increase of price stimulates the 
collier to make new trials. The difficulties, likewise, in the 
way of deep mining are mere questions of cost. It is impor- 
tant to notice that the assumption of 4,000 feet as the greatest 
depth to which coal can be worked, on account of the increase 
of temperature, is purely voluntary. The increase has been 
calculated at a rate for which there is no authority ; and while 
we are saying our coal-beds cannot be worked below 4,000 feet, 
a colliery in Belgium has nearly approached that depth, and 
no inconvenience is experienced by the miners. 
It is not my intention, indeed, to attempt to find answers to 
any of the above questions. My purpose is, seriously to show 
that answers cannot be given to most of them, without an ex- 
amination of the most searching character, which examination 
is beset with difficulties of no common order. I desire, how- 
ever, to convey to the , readers of this article a very general 
idea of the conditions under which our beds of coal have 
probably been formed, and of the disturbances to which they 
have been subjected after they have been formed, since this 
geological problem bears on the questions of working the 
