428 Review of “ Outlines of the 
are annually raised in these counties out of this formation. 
Now a ton of coal is very nearly one cubic yard; so that 
the yearly loss from mining amounts to 2. 8 millions, or 
(adding a third for waste) to 3.7 millions of yards. Accor- 
ding to this statement, the Newcastle coals may be mined 
to the present extent for 1500 years before they be ex- 
hausted. But from this number we must deduct the amount 
of the years during which they have been already wrought. 
We need not be afraid then, of any sudden injury to Great 
Britain from the exhaustion of the coal mines. It is neces- 
sary to keep in mind, likewise, that I have taken the great- 
est thickness of the coal beds. Now as this thickness is 
far from uniform, a considerable deduction (I should con- 
cejve one third of the whole) must be made in order to 
racite* and bituminous coal 
bviously referable to different 
epochs. 
Mill Stone Grit and Shale. 
beneath the coal measures an 
The shale does not 
the coal formation 
sandstone, 
These rocks lie immediately 
d alternate with each other. 
materially differ from the slate-clay of 
‘ton; and the mill-stone grit is a coarse 
consisting of quartzose particles of various sizes, 
act clliptical transition formation, (embracing the Rhode Island an- 
th : : é 
se gee from to Newpo wn 
Universi 
ity in i instructi 
we shall Se of this ellipse, may we not expect, that ere logy 
? 
