1866. | Our Coal Supply and our Prosperity. 463 
Tons. Condition. 
Vie, SUTOpPSbITe mee Mpa! F beyieth sto al snl 5) 1,135,000 (declining) 
10. Gloucestershire, Somersetshire, and Devon- 
SHiInG te AMeme startin eee »_. « 1,875,000 (ditto) 
11. South Wales coal-field (including Mon- 
INOUHISHITE eee sures cts a lush ye 12,036,507 (increasing) 
Mee NO GUNOV GLGS! ute pe kort.) (es ce, ee oes 1,983,000 (increasing) 
LSSCOLlandgma ot st Jan a halo ON SUVA 12,650,000 (increasing) 
A eelreland nate fan Hebets ci eek Oot Mae Tae es 123,500 (declining) 
The total output was 98,150,587 tons from 3,256 collieries ; 
but the present progressive or retrogressive state of any of the above 
coal-fields is not always a criterion of their resources. 
We now enter upon our second inquiry : 
Are our sources likely to extend, or may we in the course of 
time have greater facilities for obtaining coal in Great Britain, or 
from other countries, than we at present possess ? 
Tt is hardly necessary to remind our readers that upon the 
replies to this inquiry mainly depend the estimate of the probable 
duration of our coal-fields. Let us therefore ask, first: Will 
improved systems of mining and ventilation enable us to procure 
coal below 4,000 feet, calculated by Mr. Hull to be the extreme 
depth? The answer involves many important considerations. 
It may probably be admitted that high temperature can never 
prove a serious impediment to deep mining. Mr. Vivian has, we 
think, disposed of this question ;* as it is one which may fairly be 
left to the progress of invention to solve. As Mr. Vivian remarks, 
“Tf heat were produced by additional barometrical pressure, it was 
equally true that by rarefaction we produced cold;’ and he states 
that the process of rarefaction by machinery is now employed in 
the deep mines of France and Belgium. Although there ig 
therefore no reason for supposing that the calculation of Mr. Hull 
of the combined temperature of the strata and air (120° F.), at a 
depth of 4,000 feet is incorrect, yet it is one of those objections to 
deep coal-mining which may safely be dismissed. This we believe 
to be Mr. Hull’s present opinion. 
A more formidable obstacle is likely to be found in the pressure 
of the superincumbent strata. And this may be experienced, not so 
much in the greater density of the coal, as in the difficulty of 
supporting the roof and sides of the air-passages, and the “ goafs,” 
or chambers from which the coal has been extracted. Already, 
with our comparatively shallow mines, this is often a difficulty ; 
and how much greater is it likely to become, when instead of 
dealing with a pressure from 2,000 feet of strata, the depth is 
doubled. It is generally supposed that when the coal is removed 
the overlying strata form a natural arch which at first supports 
* His ‘Speech.’ Ridgway, 1866. 
