ROTTEN-STOVE. 
bed varieties of I'mestone, several ofbers occur, which, in their 
external characters, exhibit various gradations between the black 
marble and the bituminous shale, that separates the calcareous I 
beds ; and that the whole formation of these limestone slratu/a > 
appears to graduate, or to pass, by an almost insensible transi- < 
tion, into the great stratum of shale, under which the limestone i 
of Derbyshire, for the most part, dips. 
It is evident, from the above remarks on the black limestone i 
formation, that among its numerous beds the orginal of Rotten- ) 
stone probably exists ; and, though the result of my own expe- | 
riments and observations certainly does not warrant the con- | 
elusion, that it has yet been detected as a native rock or stratum, ) 
there seems little doubt, but that a more careful 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 holding, sometimes, ; 
24 per ct. of alumine, undoubtedly comes near in external cha- | 
racters to the central nodules of marble, which, it has been 
observed, occur frequently as nuclei to the fragments of hard 
Rotten stone, (v.p. 317) and which, there is every reason to |j 
conclude, are remaining portions of the original calcareous ^ 
rock. Still, however, this rock appears to have differed essen- | 
tially from the limestone, with which we are now comparing it : I 
1st. in being a somewhat softer stone ; 2d. in containing a much 
larger proportion of inflammable matter j and, lastly, in hold- 
ing, at least, 30 per ct. of alumine.* It may here, perhaps, be 
objected, that a stone, holding even 30 per ct. of alumine, can 
never be presumed to give by its decomposition, a substance 
containing more than double such proportion of the material — - 
especially as this substance is evidently wof composed (in cer- 
tain instances at least) of the travelled, and at length deposited, 
particles of the otiginal stone ; but actually exhibits the matter 
(in part) of the original stone itself under its primitive struc- 
ture, and merely (deprived of one of the constituent principles. 
• • 
• All tlif specimens I have examined, have given something more 
- than the proportion of alumine here stated. 
For 
