56 



CHAP. III. 



ON THE CLASSIFICATION OF ROCKS ADOPTED IN 

 THE PRESENT ARRANGEMENT. 



IN the progress of geological science, two differ- 

 ent plans have been adopted for the classification 

 of rocks. In one of these, all rocks are divided 

 into two classes, the primary and secondary: in 

 the other, the division is into three, namely, the 

 primitive, transition^ andjloetz; the last of these 

 being the same as the second class of the first 

 method. It is obvious therefore, that the esta- 

 blishment of a transition class is an attempt to 

 subdivide the primitive class of some geologists. 

 It is not here intended to explain or examine the 

 hypothetical views on which this subdivision 

 appears to have been founded ; as it would lead 

 to general disquisitions foreign to the subject of 

 this work. But as it has not been adopted in the 

 present arrangement, it is proper briefly to state 



