Rotten-Stone. 325 
paring it:—Ist. in being a somewhat softer 
stone. 2d. in containing a much larger pro- 
portion of inflammable matter—and, lastly, 
in holding, 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 not composed (in cer- 
tain instances at least) of the travelled, and 
at length deposited, particles of the origmal 
stone ; but actually exhibits the matter (in 
part) of the original stone itself under its pri- 
mitive structure, and merely deprived of one 
of the constituent principles.—For this really 
seems to be the state, in which the greater part 
of the indurated Rotten-stone occurs. To this 
objection, I can only, at present, oppose, as 
probable, the supposition, that, during the 
formation of hard Rotten-stone, while losing 
the calcareous particles, a gradual and consi- 
derable contraction took place in the remain- 
ing matter ; and that this was effected without 
destroying the slaty structure, where it pre- 
viously existed, in the primary stone.t By 
* Allthe specimens I have examined have given some- 
thing more than the proportion of alumine here stated. 
+ A nearer approximation of the aluminous particles to 
