Full text: Vol. II (2)

158 SILICEOUS PETRIFACTIONS AND CRYSTALS. 
is reason to be convinced that it has been introduced in a very fluid 
state, or that it has been produced in thefe strata by the action of 
some very fluid matter which has penetrated them. The proof of 
this is, our finding ſhells, lithophyta, and other marine produc 
tions, originally calcareous, but which are now completely pene 
trated by this fort of matter, and seemingly converted into flint or 
agate, without losing their external form. The fame fact is further 
establifhed by the quantities of foffil wood penetrated and petrified 
with this matter, found in many parts of the world. It is found in 
all ſtates, from that of stony wood, still combustible, to that of pure 
flint. 
It also deserves notice, that the nodules of flint found in chalk 
and lime, often in very strange forms, are not fimply lying there, 
but seem forming, or else decaying, in that fituation, being always 
furrounded by a crust, which changes gradually from a calcareous 
to a filiceous nature. 
Another curious fact relating to this stony fubstance is, that masses 
of it are sometimes found which include water perfectly inclosed in 
the hard ſtone. This has been observed in crystal, in common flint, 
and in agate. 
In whichsoever of thefe ftates the hard stones are found, when 
masses of them occur that are not folid, but have vacuities within 
them, in these we find their matter crystallized, and very often into 
remarkably regular and transparent crystals. Such are often found 
in hollows of veins, and of pebbles. They are generally columns 
of six sides, terminated by a six-sided pyramid : Or sometimes they 
are pyramids alone. All thefe crystals are chiefly found in cavities 
of veins, or of hard stones. 
I have yet to mention one other state or condition in which the 
filica has been found, and that is, diffolved in water. There is one 
very remarkable example of this in Iceland, particularly at the cele¬
	        
Waiting...

Note to user

Dear user,

In response to current developments in the web technology used by the Goobi viewer, the software no longer supports your browser.

Please use one of the following browsers to display this page correctly.

Thank you.

powered by Goobi viewer