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



which now constitute the traps and the various kinds of lava, it 

 is difficult to understand, upon this hypothesis, why the fissures 

 and cavities of the latter, should contain minerals differing entirely 

 in crystalline forms, and in many instances yielding substances 

 not known to exist in the rock from which they are said to be 

 derived.* Even granting that the constituents of these minerals 

 actually exist in the granite, the chemical mineralogist will be 

 slow to believe that, at such distant localities and in such widely 

 separated epochs, the very same, as it were, accidental segrega- 

 tion of certain substances should take place. He would be more 

 likely to infer that these minerals had previously existed, at least 

 in their anhydrous state, — that they had been liquefied by heat, 

 and that in their subsequent crystallization they were merely 

 obeying the laws of molecular attraction which regulate this 

 process. 



It may be here observed, that the reference of these igneous 

 products to ordinary granite is based upon the assumption, that 

 this latter rock not only constitutes the floor of all the strata 

 which have been observed, but that it forms the nucleus of the 

 globe. But after all, do not the trappean rocks and minerals 

 show a difference in composition, as well as in the arrangement 

 of their constituents ? Are not these, as well as our modern lavas, 

 the representatives of series of rocks or of materials, whether solid 

 or liquid, differing considerably from granite? If they are so, 

 then with the knowledge which we possess in regard to the deep 

 seated source of volcanic action, we may conclude that the lavas 

 ejected by volcanoes, and the trappean rocks which resemble 

 them, although found in the cracks and fissures of the most recent 

 strata, in fact belong to a series lower than any which we see 

 upon the surface of the earth. And perhaps by a close examina- 

 tion of the chemical theory of volcanic eruptions, we shall be 

 enabled to comprehend the differences to which we have referred, 

 especially if we are willing to admit that the conditions of these 

 modern eruptions were different from those which characterized 

 the older ones. 



* " Admitting this prevalence of granitic compounds at the earliest periods, their 

 production at more recent epochs shows that the conditions necessary for their for- 

 mation continued up to such epochs, though they may have been infinitely more 

 rare, having in a great measure given place to those under which the more com- 

 mon trappean rocks were produced." — De la Beche, 475, Am. ed. 



