M I N fi R A L O G Y. 3X 
SEC X XXV‘: 
E. Calcareous Earths blended with an argilla- 
ceous earth, ^erra calcarea argilla intimh 
mixta. Marie, Marga. 
1. When crude, it makes an efFervefcencc 
with acids, but 
2. Not after having been burnt ^ by which 
operation it is obferved to harden, in pro- 
' portion as the clay exceeds the calcareous 
fubftance. 
3. It eafily melts by itfelf into a glafs, and 
even when it is mixed with the moll re- 
fra6tory clay. 
4. It is of great ufe in promoting the 
growth of vegetables, lince the clay tem- 
pers the drying quality of the calcareous 
earth. 
5. When burnt in' a calcining heat, it rea- 
dily attrails water : and, expofed to the 
air, in time, it falls into a powder. 
The varieties of this kind, worthy to 
be taken notice of, depend on the dilfer- 
cnt quantities of each of their component 
parts, and on the quality of the clay. I 
Ihall, for inllance, fpecify the following 
examples, 
SECT. XXVI. 
I. Loofe and compacl, Marga friahiUs. 
I'his dilTolves in water like common clayT 
of their parts, fubjefl to the fame varieties as the other fpecies 
of lime-fione : and it is to be obferved, that a volatile alcali 
is commonly fuppofed to have entered into the compofition of 
the fcetid ftones, though it has never yet been difcovered by 
any experiment. 
a. Reddilh 
