1, as ehibited in New York. 337 
suppose, that a large bed ctptimeatinie may have been subjected 
toa degree of heat sufficient to soften or fuse sundry imbedded 
minerals, without causing any marked alteration in the chemical 
composition of the rock. Nor is it difficult to understand how 
those rocks in the immediate vicinity of the source of heat, or of 
the heating mass, should exhibit appearances quite different from 
those more remote. Thus we may account for the fusion of cer- 
tain minerals in the white limestone and the gneiss, while in 
those found in the mica slate there is no apparent change. ‘Thus 
also, there isan explanation of the fact that one part of a lime- 
stone bed may be dolomitized, while another remains in its sup- 
62 original condition. 
n proceeding to the consideration of other evidences of igneous 
action, I may observe that there is one circumstance applicable to 
all the minerals found in the primary masses, with the exception 
of serpentine, too striking not to deserve particular attention. I 
refer to the absence of water, at least in any thing like atomic 
proportions, as one of their constituents. When it is recollected 
that this substance is a common ingredient of those minerals 
which are found in fissures of trap and greenstone, and in the 
lavas which have been ejected from volcanoes, we may perhaps 
infer with safety, that water was not evolved from the central 
nucleus during the earlier geological eras. 
I have said that serpentine is an exception to the wines 
just made, in regard to the absence of water in the minerals of the 
primary masses. Now serpentine, which is oftentimes very abun- 
dant in white limestone, and exists even in extensive beds, con- 
stantly contains from ten to twenty per cent. of water. 
Several foreign localities are described which exhibit the change 
of trap into serpentine, and others in which dykes and masses of 
Serpentine occur under circumstances similar to those of trap rock. 
Facts of a similar kind, are observed in the state of New York. 
Thus on Staten Island, serpentine forms the main ridge of hills, 
and extends nearly eight miles in a direction N. 20° E. and 8. 
20° W. It assumes a variety of aspects, and contains hydrate 
and carbonate of magnesia, asbestus, &c. The prolongation of the 
line of direction strikes the serpentine hills of Hoboken, which 
are similarly characterized, and hand specimens of which can 
Searcely be distinguished from those obtained on Staten Island. 
On the west of this range is the trap - which is exposed for 
Vol. xzv1, No. 2.—Jan. -March, 1844. 
Prof. Beck on Igneous A 
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cae 
