1818.] ON THE FORMATION OF ROCKS. o37 



ORDER I. 



Those rocks which conjecture might be disposed to 

 place in the rocks of the Neptunian origin. 



Gneiss by its extensive and regular stratification 

 agrees with the relative situation of all Neptunian 

 rocks^ but it differs widely in the arrangement and na- 

 ture of its component parts from any rocks known by 

 actual observation to be of Neptunian origin : it equal- 

 ly differs from those rocks placed by direct analogy 

 in the Neptunian class, though it agrees with the 

 Neptunian in having many and rich metallic veins in- 

 tersecting it. This perhaps is one of the most promi- 

 nent marks of distinction between the two origins of 

 fire^ and water. 



Mica Slate being a species of gneiss, where the 

 layers of feldspar or quartz are so small as not to be 

 distinguished by the eye, must of course follow the 

 origin of the gneiss, as it frequently runs by im- 

 perceptible gradations into gneiss, and gneiss into 

 mica slate, making it difficult to decide where the one 

 begins, or the other ends. 



Primitive Limestone frequently alternates with 

 gneiss, and resembles the Neptunian origin in its re- 

 gular and extensive stratification. It docs not differ 

 much in its structure from other limestone formed by 

 water, such a^ the stalactites in caves. It therefore 



