64 



and can lead to no improper associations of ideas 

 respecting the formation of the earth. The pri- 

 mary class is thus considered simply as anterior 

 in date to the secondary ; and all rocks therefore 

 become divided into two leading classes, the Pri- 

 mary and the Secondary. 



Each of the two classes is subdivided into two 

 divisions, the stratified and the unstratified, dis- 

 tinguished, respectively, by that difference of 

 disposition, which is indicated by these terms. 

 As these subdivions have not yet been introduced 

 into any of the arrangements of rocks, they will 

 each require some explanation. 



In the first class, all the modifications of gra- 

 nite are considered as entering into the uristrati- 

 fied division ; together with serpentine. The 

 reasons for not including porphyry in it, will ap- 

 pear in considering the second class. 



Granite is disposed in large irregular masses, 

 from which, veins are often found to proceed and 

 to penetrate the stratified rocks in its vicinity ; nor 

 has it yet been observed in any instance to be de- 



