Prof. Beck on Igneous A tio 2, aS exhibited in New York. 339 © 
proofs which are here exhibited. But if this is the correct view, 
how happens it that while all the minerals of the granite, gneiss 
and limestone, are destitute of water, the serpentines are almost 
always loaded with that substance? Is it because the strata 
were covered with water during the period of the extrusion of 
serpentine, a condition which did not exist when the other min- 
erals were first crystallized, or when they received the broken, 
bent, rounded and slaggy forms and appearances which they every 
where present? Or is it because in later geological periods, water 
Was a more constant accompaniment of the erupted matter? 
These are questions upon which, perhaps some light may be shed 
by a reference to the composition of the minerals found in certain 
trappean rocks, as compared with those which are known to be 
the products of true volcanoes. 
In the 17th volume of the London, Edinburgh and Dublin 
Philosophical Magazine, Dr. Thomas Thomson has given a de- 
tailed account of the minerals occurring in the Kilpatrick hills, 
which bound the valley of the Clyde from the Stokey Muir to 
Dumbarton. These hills are composed of various trap rocks, 
among which amygdaloid is pretty common. The cavities of this 
variety are usually filled up by crystallized minerals, many of 
which, though not the whole, belong to the zeolite family.. Dr. 
Thomson divides the minerals found in these hills into two sets. 
Ist. The zeolites, so called, because they froth before the blow- 
pipe, and they owe this frothing property to the great quantity of 
water which they contain, and which is easily driven off by heat. 
2d. Minerals nearly destitute of water, which in general, although 
not in all cases, exist in greater quantities than the zeolites, and 
may be often considered as constituting an integrant portion of 
the substance of the mountain in which they occur. 
Thirteen of these zeolites are enumerated, viz. stellite, hom- 
Sonite, natrolite, scolezite, glottalite, laumonite, chabazite, anal- 
cime, Cluthalite, stilbite, Heulandite, harmatome and Phillipsite. 
se are chiefly silicates of alumine and lime, and they contain 
from two to six atoms of water. To these may be added, prehnite, 
datholite, apophyllite and Morvenite, which also contain water as 
one of their constituents. 
We have only to examine a list of the minerals found at Bergen 
Hill, Paterson, and Bound Brook in New Jersey, at Piermont in 
New York, and in the trap rocks of Massachusetts and Connecti- 
