180 On the geological Theory supported by Mr. Smithson, 
Fragments being only used for the common purposes, the mary 
who entered these cavities broke with his hammer all the pro- 
jecting prisms around it; and the quantity was sometimes so 
great, that the associates made much money from what they ob- 
tained in one of them. Such are the general circumstances con- 
cerning rock crystal found in that kind of schistose strata; but 
the particulars to which I now come, are. no less important to 
the natural history of that mineral, 
I shalt mention as a first important circumstance, the size of 
some prisms which have been found, I have known two prisms, 
one of which was perfectly transparent, employed im a most beauti- 
ful work for the late Empress Queen, which prism was from 9 to 
10 inches in diameter: the other, less transparent, was above one 
foot. _I think I can now say with more certainty than the 
author has done for his hypothesis, that swch crystals have never 
been seen as the product of fusion. But the character of true 
conclusions from the phenomena, is manifested by the coincidence _ 
of circumstances in the same object; and it is the case in the 
system of the aqueous origin of our mineral strata: a confirma- 
tion to which 1 now come. 
As the men who followed this pursuit knew also that some 
curious travellers in the Alps paid them for the trouble of detach- 
ing parts of the crust covering the sides of the cavities with its 
prisms,—which erust, by naturalists of many countries, is called 
druses,—they carefully detached them; and we had the oppor- 
tunity of purchasing many which are in our collection of mi- 
nerals remaining at'Geneva. Now, in these druses, many proofs 
are found that they were formed in cavities during the time that 
our continents constituted the led of the sea, and that conse- 
quently these cavzies were filled with water. That great geo- 
logical fact, so contrary to the igneous system of the author, is 
demonstrated by the immense quantity of marine exuviee found 
in the strata commonly called secondary. 
By the inspection of the druses that we have in our collection, 
it is impossible not to be conyinced that the prisms have been 
formed, not only in caviéies filled with water, but by a process in 
which each prism increased successively in size by new addi- 
tions; and that they were as shooting at the same time in dif- 
ferent directions from the same points. In one of these druses a 
large prism, in its increase of size, has enveloped a small one ; 
they are both very transparent ;.and this phenomenon might be 
overlooked, did not the small prism project on one side of the 
other: but this circumstance directing the sight in the large 
prism, the small one.is seen in it by the different refraction of the 
light. In another druse, by some change in the successive pro- 
cess of crystallization, a large prism has divided itself into small 
enes, like the branches of a tree. It 
