324 Cursory Remarks on 
the black-marble and the. bituminous shale, 
that separates the calcareous beds; and that 
the whole formation of these limestone stratula 
_ appears to graduate, or to pass by an almost 
insensible transition, into the great stratum of 
shale, under which the limestone of Derby- 
shire, for the most part, dips. 
It is evident, from the above remarks on 
the black-limestone formation, that among its 
numerous beds the original of Rotten-stone 
probably exists ; and, though the result of my 
own experiments and observations certainly 
does not warrant the conclusion, that it has 
yet been detected as a native rock or stratum, 
there seems little doubt, but that a more care- 
fal examination, than what my leisure when at 
Ashford permitted me to make, may hereafter 
determine the stone in this state. The variety 
of black limestone already described, as hold- 
ing, sometimes, 24 per ct. of alumine, un- 
doubtedly comes near in external characters 
to the central nodules of marble, which, it 
has been observed, occur frequently as nuclet 
to the fragments of hard Rotten-stone, 
(v. p. 317.) and which, there is every reason to 
conclude, are remaining portions of the 
original calcareous rock. Still, however, this 
rock appears to have differed essentially from 
the hmestone, with which we are now com- 
