SO GEOLOGY. 



much evidence to render this more than probable this 

 fluidity was apparently caused by intense heat. The 

 consolidation of this fluid might have been produced 

 by the radiation of heat from its surface, the result of 

 which might be a crystallization, and formation of a 

 shell of granitic rocks round a nucleus of melted matter 

 of a heavier nature than granite. 



In viewing a vertical section of the earth's crust, it 

 will be perceived that the materials of which it is com- 

 posed are not thrown together confusedly, but are 

 arranged in a most beautiful order, generally forming 

 layers or strata, surrounding the globe like the coats of 

 an onion, yet not perfectly horizontal, the lower ones 

 particularly having such an inclination that they all 

 occasionally appear on the surface. 



The ingredients which compose the various strata are 

 found to differ both in their nature and manner of for- 

 mation ; for while some are of a crystalline, or vnstrati- 

 fied character, others are sedimentary or stratified. In 

 the newer rocks the remains of animals and plants are 

 found in a fossil state, while in the older rocks there 

 are no such remains. Geologists, therefore, have availed 

 themselves of these circumstances to form a division 

 of the earth's strata ; that series of rocks which did not 

 contain organic remains they called Primary, and those 

 which did contain organic remains they called Secondary; 

 each of these being again variously subdivided. They, 

 however, differ in this respect, some making three 

 divisions, and some more, even six and seven. In this 

 treatise there are assumed to be four divisions, the Pri- 

 mary, the Transitive, the Secondary, and the Tertiary. 



PRIMARY ROCKS. 



The lower, or primary rocks, are divided into the vn- 

 straiified and the stratified. The former, from their crystal- 

 line character, and appearance of having been acted upon 

 by intense heat, are termed Igneous or Plutonic rocks ; 

 the latter, from their being a deposition from water, are 

 termed Aqueous, or Sedimentary. 



