Z4 FIRST GEOLOGICAL EPOCH GRANITE. 



12. As already stated, at As origin our globe must have been. a 

 mass kept in a state of fusion by the action of heat, and its surface 

 became solid by slowly cooling. This first crust must have re- 

 mained for a long time in a soft or pasty condition, and at first its 

 temperature must have been too high to permit water to remain 

 on its surface without evaporating. It must have been split in 

 different directions by the contraction produced by cooling, and 

 then resembled the masses of ice which in our day cover the sur- 

 tice of the polar seas ; that is, it presented a very unequal surface, 

 studded with immense fragments heaped up in all directions. In 

 this first geological epoch were formed the massive rocks, such as 

 granite, w T hich serves as the base of all other rocks, and is the 

 result of the solidification of mineral substances previously melted 

 by heat. The cooling of this first crust must have also caused 

 the precipitation of the least volatile matters diffused in the atmo- 

 sphere, just in the same manner as a cold body placed in a warm 

 moist air is quickly covered by a layer of condensed vapour ; and 

 from this cause came new changes in the configuration of the sur- 

 face of the globe, and the formation of new beds of a crystalline 

 texture. 



13. The most ancient portion of the crust of the earth known 

 to geologists is composed chjefly of granite and some other un- 

 stratified rocks which appear to be also of igneous origin. 



14. We give the name of granite to a rock, which is extremely 

 hard, having a rough fracture, which is composed of a confused 

 agglomeration of crystals formed of three distinct materials: some 

 of these crystals have a glassy appearance, and are ordinarily of 

 a grayish colour; they are quartz, the same material of which 

 rock crystal is composed ; others, often large, opaque, and some- 

 times rose-coloured, sometimes green, sometimes white or yellow, 

 are formed of a mineral co\\e& feldspar ; and the third variety of 

 crystals, which are composed of mica, resemble small brilliant 

 spangles, sometimes black, and sometimes silvery white. Granite 

 then consists of quartz, feldspar, and mica. Certain varieties of 

 granite remain for centuries exposed to the inclemencies of the 

 weather without undergoing any alteration ; but other varieties are 

 speedily disintegrated by the action of the atmosphere, and are thus 

 reduced to a kind of grit or argilla'ceous earth. It presents no 

 trace of stratification, and possesses all the characters of a rock of 

 igneous origin. 



12. What is supposed to have been the condition of the earth when first 

 formed? What was the condition of the crust of the earth when first 

 formed ? Was it smooth and regular? 



13. Of what is the most ancient portion of the crust of the earth com- 

 posed ? 



14. What is granite? Of what minerals is it composed 7 What is th 

 character of granite for durability ? 



