_-separated in an insoluble state,) and to carbonate of soda. 
182s T. S. Hunt on the Chemistry of Natural Waters, — 
i 
i 
a 
ing the lime and magnesia as carbonates, liberates the silica ina 
soluble form; while the iron and manganese, passing toa ste 
of higher oxydation, remain behind, unless the action of organit — 
matters intervenes to give them solubility. Me 
§ 18. It is to be remarked that, apart from the peculiar and 
complete decomposition resulting in the production of kaolin,t0 
which orthoclase, oligoclase, and some other feldspathides, a 
leucite, beryl, and perhaps also the scapolites and albite are oe 
casionally subject, orthoclase is less liable to change than the 
soda-feldspars, albite, oligoclase and labradorite. Weathered sit 
faces of these become covered with a thin, soft, white and 
opaque crust, from decomposition, while the surfaces of ortho 
clase under similar conditions still preserve their hardness and 
translucency. The decomposition of feldspathides, and othe 
aluminous double silicates, whether rapid and complete, or slow : 
and partial, apparently yields the same results. A gradual pro 
cess of this kind is constantly going on in the feldspathic mi 
ters which form a large proportion of the mechanical sediments : 
of all formations; and in deeply buried strata is not impro ie 
accelerated by the elevation of temperature. The soluble alka 
line silicate resulting from this process is in most cases cece 
ed by carbonates of lime and magnesia in the sediments, gi 
ing rise to silicates of these bases, (which are for the gree 
im rare cases does potash appear in large proportion among the 
at 
bit EF i 
ee if 
agent in decom posing feldspathic minerals.” The solvent ach 
oid waters charged with carbonic acid is undoubted, as shoN 
arious experimenters, especially by the 
- this acid is not ilictige cteasit fer abee quantities required. 
Proportion of it in atmospheric waters is so inadequate © ihe 
mes necessary to suppose some subterranean sot of natro 
gas, which.is by no means a constant accompaniment 
spr id is observ’ 
Prings. A copious evolution of carbonic aci oo 
* Bischof, Chem. Geol., i, 181. © This Journal, (24 iy 
