- Artificial Production of Minerals. — Bld 
‘in many of the crystalline limestones which remain to us as 
perpetual witnesses of the ancient exhalations emanating from 
the neighbouring eruptive rocks. Sometimes the effect has 
‘been more complete ; and even the primitive mass may have 
disappeared, in the state of soluble chloride, as well as the 
water which has formed the oligistic iron of volcanoes. 
If we turn from the example of crystalline limestones and 
dolomiies richest in minerals, to those of St Gothard, Sweden, 
Finland, and the United States, we perceive that the presence 
of chlorides mingled with fluorides, and sometimes sulphur- 
ated compounds, accounts for the formation of their most 
characteristic minerals. We must include, in this explana- 
tion, the rich deposits of red oxidated zine, with the Franklin- 
ite of New Jersey, as well as diverse masses of oligistic 
iron and oxidulated iron, which have also been produced in 
the limestone. 
We see magnesian compounds, such as spinelle, bcm 
dite, mica, pyroxine, amphibole, warwickite, and serpentine, 
accumulated sometimes with marked predominance, in lime- 
stones which contain no magnesia. This fact, hitherto un- 
explained, should be regarded as a consequence of the differ- 
ent chemical affinities of lime and magnesia; for we always 
find, in our experiments, the chloride of magnesium to be 
precipitated by lime ; and when both these bases are in con- 
nection with chloride of silicium or aluminum, the lime 
yields its oxygen, and the magnesia, remaining in the state 
of oxide, enters by preference in the oxidized combination 
with the regenerated silica or alumina. The same principle 
explains the presence of the magnesia to the exclusion of the 
lime, in the oxidulated irons. Must we ascribe to the same 
cause the preponderance of the magnesia over the lime in the 
elements of granite and serpentine ? 
_ The causes to which quartz and silicates owe their pre- 
sence, principally in granitic rocks, has long been a difficulty 
in all the hypothesis of the formation of the primordial sys- 
tem of rocks. But, we now perceive in our experiments, that 
the quartz crystallizes at the same time, and even later than 
the silicates, at a temperature which scarcely exceeds the 
