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



cut, to satisfy ourselves that these hydrous forms are by no means 

 confined to one region or district, but seem at least in general to 

 characterize the less ancient exhibitions of igneous action. 



If the question be now asked, whether the occurrence of these 

 minerals, from which the water can be expelled by moderate 

 degrees of heat, is not inconsistent with the idea that the whole 

 rocks were ejected in a molten state, I refer the inquirer to the 

 products of volcanoes. Nearly one hundred species of minerals 

 are enumerated as occurring among the lavas of Vesuvius, and a 

 considerable number of these are characterized by their containing 

 water as one of their atomic constituents. I may here refer to 

 Gehlenite, Davyne, mesotype, Comptonite, sulphate of ammonia, 

 potash and soda — alum, &c. Nor need we be long in doubt as to 

 the source of this water, when we see steam frequently ejected 

 from volcanoes, and various compounds of hydrogen among their 

 products. 



I have thus noticed the difference in the effects of heat as ex- 

 hibited in the minerals found in the older rocks and in those of 

 more modern eras, and have offered some suggestions in regard 

 to the cause of this difference, drawn chiefly from the total ab- 

 sence of water in the one class, and its frequent presence in the 

 other. Let us now see what use can be made of the facts here 

 brought forward, in determining the nature of those rocks which 

 are commonly supposed to be the " floor" upon which the strata 

 are deposited. 



All geologists agree that the unstratified rocks " are generally 

 of the nature of granite, that is to say, largely crystallized aggre- 

 gates of feldspar, with variable admixtures of mica and quartz, — 

 or more rarely quartz and hornblende, — or quartz and hyper- 

 sthene." Granite is now considered, in whatever variety it may 

 present itself, " as an older rock than any of the strata which 

 rest upon it." It is not, however, as was formerly supposed when 

 granite was thought to be of aqueous origin, necessarily the pro- 

 duct of an anterior epoch. There seems now to be no doubt, 

 "that in very many cases the granite has been in a state of fusion 

 since the deposition of several of the older formations, so that it 

 has actually been injected into the fissures and cracks of these 

 strata, or been raised up in a fluid mass among them." In the 

 language of Mr. Phillips, whom I have already quoted — " We 

 may, therefore, consistently admit granite as well as other igneous 



