GEOLOGY. 



11 



CHAPTER 11. 



GEOLOGY. 



THE ORDER AND ARRANGEMEMT OF THE ROCKS. 



Geology informs us that there is no portion of the surface 

 of our planet that has not been immersed in the waters of the 

 deep. It is also an acknowledged principle of the science, 

 that there is no portion of the earth's surface that has not 

 been under the influence of fire or the action of subterranean 

 heat. The whole superficial crust of the globe, it therefore 

 follows, is composed of two great systems of rocks, namely, 

 those which are sedimentary or stratified, and those which are 

 termed igneous or unstratified. All sandstones, hmestones, 

 and shales belong to the former class ; the granites, traps, and 

 lavas are all ranged under the latter class. They are termed 

 primary, secondary, and tertiary, according to their geological 

 age or order of superposition. 



The following table exhibits both divisions, and their sub- 

 divisions according to their mineral constituents, chronological 

 order, and relative superposition : — 



