212 PREVAILING THEORY CONCERNING [Ch. XL 



CHAPTER XI. 



A SKETCH OF THE PREVAILING THEORY CONCERNING THE 

 NATURE OF THE PRIMARY ROCKS. 



Two classes of the primary rocks the stratified and unstratified the former 

 of aqueous, the latter of igneous origin. The whole Earth originally 

 igneous the granitic rocks the result of its secular refrigeration. Igneous 

 rocks of three kinds granitic trappean and volcanic. Granite a rock 

 of all ages. The crystalline strata associated with granite also belong to 

 various epochs supposed to be altered or metajnorphic rocks. The deter- 

 mination of the precise age of an individual mass of granite. De Beau- 

 mont's theory concerning the relative ages of mountain-chains not generally 

 received. Granite protruded in a solid as well as in a fluid state. The pre- 

 vailing theory a modification of that of Hutton appears to be objectionable. 



Lyell's statement of this theory abridged The nature of the objections 



about to be advanced and the order in which they are proposed to be dis- 

 cussed. 



FOLLOWING the plan adopted in the preceding chapters, of 

 endeavouring to make this work interesting even to those 

 who are not professed geologists, it is now proposed to give a 

 brief sketch of the prevailing theory concerning the nature 

 and origin of the primary rocks. And, indeed, such a mode 

 of proceeding may, perhaps, meet the approbation of the 

 most experienced, as it will place the succeeding discussion 

 on a more tangible basis, and diminish the chance of any 

 misapprehension. 



According to the most generally received opinion, the pri- 

 mary rocks are divided into two grand groups or classes, the 

 stratified and the unstratified : the former comprising various 

 kinds of gneiss, mica-slate, and other schistose rocks; the 

 latter, all the granitic and massive rocks commonly associated 

 with the former. These groups are supposed to have had 

 very different origins ; the one being of aqueous, the other of 

 igneous formation. Thus it is presumed that the stratified 



