COAL AS A RESERVOIR OF POWER. 
159 
fields. At a period in geological time, when an Old Red Sand- 
stone land was washed by ocean waves highly charged with 
carbonic acid, in which existed multitudinous animals, whose 
work in nature was to aid in the building up masses of lime- 
stone rock, there prevailed a teeming vegetation from which 
has been derived all the coal-beds of the British isles. Our 
space will not allow of any inquiry into the immensity of time 
required for the growth of the forests necessary for the produc- 
tion of even a single seam of coal. Suffice it to say, that 
within one coal-field, we may discover coal-beds to the depth 
of 6,000 feet from the present surface. The section of such a 
coal-field will show us coal and sandstone, or shale, alternating 
again and again — a yard or two of coal and hundreds of feet of 
shale or sandstone — until we come to the present surface ; 
everyone of those deeply-buried coal-beds having been at one 
time a forest, growing under the full power of a brilliant sun* 
the result of solar forces, produced then, as now, by chemical 
phenomena taking place in the sun itself. Every cubic yard of 
coal in every coal-bed is the result of a very slow, but constant, 
change of a mass of vegetable matter ; that change being analo- 
gous to the process of rotting in a large heap of succulent 
plants. The change has been so slow, and continued under a 
constantly increasing pressure, that but few of the gaseous con- 
stituents have escaped, and nearly all those physical forces 
which were used in the task of producing the woody matter of 
the plant, have been held prisoners in the vegetable matter 
which constitutes coal. How vast, then, must be the store of 
power which is preserved in the coal deposits of these islands ! 
We are now raising from our coal-pits nearly one hundred and 
ten millions of tons of coal annually. Of this quantity we are 
exporting to our Colonial possessions and Foreign parts about 
ten million tons, reserving nearly a million tons of coal for our 
home consumption. Not many less than one hundred thousand 
steam boilers are in constant use in these islands, producing 
steam, — to blow the blast for smelting the iron ore, — to urge the 
mills for rolling, crushing, and cutting with giant power, — to 
twirl the spindle, — and to urge the shuttle. For every purpose,, 
from rolling cyclopean masses of metal into form to weaving 
silky textures of the most filmy fineness, steam is used, and 
this steam is an exact representative of the coal employed, 
a large allowance being made for the imperfections of human 
machinery. This requires a little explanation. Coal is a com- 
pound of carbon, hydrogen, oxygen, and nitrogen, the last two 
elements existing in quantities so small as compared with the 
carbon, that they may be rejected from our consideration. The 
heat which we obtain in burning the coal is almost all derived 
from the carbon ; the hydrogen in burning produces some heat* 
