1800.] 
lime-stone hills, and from its existence on 
both sides, (though not on the hills 
themselves,) of equal thickness, and 
similar in the disposition and quality of 
the different beds ; namely, that the ccal 
had once heen continued across the 
space now occupied, by these hills, and 
consequently, that the formation of these 
hills was posterior to the formation of 
the coal. It appears also, from. the 
rearing of the beds of lime-stone, and 
their broken and irregular position, that 
their present form and ‘state could not 
have been the effect of any gradual ope- 
ration of nature, but of some sudden and 
violent effort, or earthquake. Neither 
could this elevation and ruptuye of the 
inferior strata, be effected without the- 
elevation and rupture of the superior 
strata; among which is the coal, which 
accordingly dees now appear to be. still 
more disturbed, and broken into minuter 
fragments, in proportion as it is of less 
solid texture than the stone. That part 
of the coal more particularly, which im- 
mediately lay upon the ridge of the ele- 
vated country, that is, where the hills 
now appear, would be most shattered, 
and being, by its elevation, most exposed 
to the action of winds and _ floods, 
would, in time, be worn and washed away, 
and leave nothing but the harder rock, 
which now remains, 
When the elastic vapour and air, that 
were the inmediate cause of the earth- 
quakes, and elevation of the strata, be- 
gan to lose their force, either by escape 
at the fractared tops, or by condensation 
from cold, the weight cf the incumbent 
strata would incline them to subside; 
and this subsidence being resisted more 
in some places, and in others less, by the 
greater ort less cohesion and support, 
would occasion still greater irregularities 
In the fractures; and to this cause; no 
less than to the elevation, I am inclined 
to impute those frequent and extensive 
fissures, and sudden depressions of the 
coal, which I have described as being 
known under the name of faults, falls, 
and slips. 
In consequence of the unequal ele- 
vation, and subsidence, of the coal, many 
regular vacuities must have been left, 
which afterwards have been filled up 
with argillaceous and rocky matters, 
that have been washed into them, and 
become more or less consolidated. And 
accordingly, these matters do now ap- 
pear in the forms which they received 
from the vacuities, corresponding with 
- the irresularities of their surface, to the 
disjointed bottom of the coal, and forme. 
Montury Mac. No. 192. 
Mineralogy of the South-West of Sta ordshire, 
405 
ing, in. some places, rocky ridges, which 
seem to rise up into the coal, the thick- 
ness of which is there diminished ; or to 
spread itself horizontally between the 
beds of cual, which are accordingly in 
those places separated to a greater or 
less distance. The colliers generally ex- 
press themselves, as if the disposition 
and thickness of the coal, had been re-- 
gulated by the rocky bottom; but, in my 
opinion, the reverse of this notion is the 
truth. , 
The most. singular and extensive 
vacuity in the coal of this country, now 
filled up, with clay and argillaceous rock, 
is that occasioned by the separation of 
the two upper beds of the main-coal, 
which I have already mentioned under 
the name of the flying-reed, and wlica 
begin to part from the lower beds of the 
coal at Blomfield colliery, from whence 
they continue to diverge for several 
miles, until they crop out at the surface, 
and are lost at Bilstone. The separation 
of strata, originally contiguous, and the 
siibsequent. interposition of adventitious 
matter, is a very curious fact in the his- 
tory of the earth. A remarkable instance 
of this kind is observed in many parts of 
the peak of Derbyshire; where extensive 
beds of toad-stone are inserted between 
strata of lime-stone, the corresponding 
‘fissures, and metallic veins, of which, 
(not being continued through the inter. 
posed toad-stone,) demonstrate the ori- 
ginal contiguity of those strata. Mr, — 
Mitchel ascribes the great extent of 
earthquakes, ‘to the great facility with 
which the elastic fluid forces its .pas- 
sage between, the , horizontal . strata, 
which, however, it must break through 
by degrees, before it can discharge itseli. 
L have already mentioned, that ihe 
coal does not crop out in its approach to 
the Rowley hills, as it does tothe Dud- 
ley lime-stone lulls; and consequently, 
that 1t continues its course, some way at 
Jeast, under them, on both sides, tf it 
does not pass upinterruptedly, from one 
side to the other, as the culliers generally 
believe, but. which cannot be ascertained 
on account of the mass ef earth and 
basaltic-stone, which form these hills. 
The formation of these basaitic hills is 
much more difficult to explain than that 
of the lime-stone hills ; fur we know that 
the latter are part of strata, that extend 
themselves horizontaily over a great 
tract of country; but which, in some 
particular places, are elevated from their 
inferior situation, by some violent con- 
vulsion, of which we see manifest indi- 
cation, both in their own dislocated 
30 state, 
