Formation of Crystals in Geodes. 283 
_ Even the two new fluids,* recently discovered by Dr. 
Brewster, in the cavities of minerals, immiscible as they 
are, and possessed of such remarkable physical properties, 
but existing in such minute quantities, as to be discernible 
(if we are not deceived) only by the aid of powerful mi- 
croscopes, can scarcely aid us in explaining the solution of 
earthy bodies; unless indeed this very curious and impor- 
tant discovery should lead to the conclusion, that these 
fluids and possibly others exist, in minerals, in very consid- 
erable quantities. 
These reflections were suggested by an accidental ob 
servation, recently made by Mr. Bennet F. Northrop of 
the senior class in Yale College. He was occupied in 
breaking the ballast stones, thrown ashore from a vessel, 
which arrived at this port from New-Orleans, where it is 
supposed the stones were obtained. They were chiefly 
pebbles, consisting of hornstone, flint, chalcedony, and 
quartz. Many of them contained cavities lined with crys- 
tals of hyaline quartz. Some of the cavities were occu- 
pied by mammilary chalcedony, and others by a white 
spongy deposite, resembling an earthy precipitate. On 
breaking an ovoidal pebble of hornstone, whose diameter 
was three inches by two, Mr. N. was surprized to find, in 
fhe centre of the stone, a cavity of three fourths of an inch 
by half an inch, filled with a milky fluid, having very 
much the appearance of water, in which magnesia is sus- 
pended. Not expecting such a circumstance, he unfortu- 
nately spilled the greater part of the fluid, and before the 
remainder could be secured, it was exhaled (it being a 
very hot day) by a rapid evaporation, leaving a white 
spongy precipitate, lining the cavity, and staining the sur- 
faces produced by the fracture. While this rapid evapora- 
tion was going on,minute prismatic crystals shot frum the flu- 
id, even under the eye of the observer, occupying not only 
parts of the cavity, but also of the surfaces of the fracture. 
Both the crystals and the spongy mass were easily ascertain- 
ed to be silex. They neither effervesced nor dissolved in 
acids, and when rubbed between surfaces of glass they 
took hold of it with great eagerness, instantly depriving 
it of its polish, and scratching it as distinctly as a file does 
1ron. 
* See Edin. Philos, Jour:, Vol. ix. p. 94, 
