Prof. Beck on Igneous Action, as exhibited in New York. 337 



suppose, that a large bed of limestone may have been subjected 

 to a 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 is an explanation of the fact that one part of a lime- 

 stone bed may be dolomitized, while another remains in its sup- 

 posed original condition. 



In 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 statement 

 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 S. 

 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 

 scarcely be distinguished from those obtained on Staten Island. 

 On the west of this range is the trap rock, which is exposed for 



Vol. xlvi, No. 2.— Jan.-March, 1844. 43 



