456 Mr. Henry on the Natural Hi/lory, &c. 
acid. Calcareous earth has indeed been dif- 
covered, in the neighbourhood of Bath, in the 
ftate of quicklime, though, probably, not 
wholly diverted of aerial acid. But they are all 
more frequently found combined with other 
fubftances, forming faline compounds, or, one 
or more, mechanically mixed with each other, 
conftituting fpecies and varieties. 
The late Dr. Lewis, has confidered the earth 
which is obtained from vegetables, after in¬ 
cineration, and wafhing, as of the fame nature 
with Magnefia: and if we endeavour to trace 
the origin of magnefian earth, it may appear 
not improbable that, as all calcareous earth is 
the refultof the deftruCtion of teftaceous animals, 
fo the magnefian arifes from vegetables, which 
have perilhed, and undergone fome procefs 
in the great laboratory of nature; whereby 
they are reduced to this ftate. By putrefaction 
they are altered to a fine black Mold. And it 
may be that, Nature, who often operates by 
flow and fecret fteps, may make fuch further 
changes, as to convert this Mold into mag¬ 
nefian earth. 
But the origin of magnefian earth is fo con¬ 
nected with that of fea fait, which it always 
accompanies, that it may not be improper to 
confider them together; as it is probable that 
they are both formed under fimilar circumftances, 
and at the fame time. 
Philofopher$ 
