Prof. Beck on Igneous Action, 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. 

 1st. 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, Thom- 

 sonite, natrolite, scolezite, glottalite, laumonite, chabazite, anal- 

 cime, Cluthalite, stilbite, Heulandite, harmatome and Phillipsite. 

 These 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 Connect!- 



