1«18.] ON THE FORMATION OF ROCKS. ^ 



©f rocks^ one runs the risk of genei-alizing too mucli ia 

 the present state of our knowledge, and of finding the 

 greater part of future discoveries, contradicting our 

 principles of generalization. 



The metallic repositories contained in the rocks of 

 Neptunian origin^ have a great resemblance, both in sub- 

 stance and situation, to those found in the primitive 

 class; it is perhaps one of the strongest features of cgr- 

 nection which approximates those two classes, and 

 will be considered along with the rocks of the primi- 

 tive class. 



The volcanic rocks are rather more embarrassing, not 

 from the nature of the rocks themselves^ which in situ- 

 ation are consistent and uniform, and in texture, and ex- 

 ternal characters, better marked, united by stronger fea- 

 tiu'es of family connection, than tiie Neptunian rocks—. 

 but from the complicated state of tlie nomenclature, ar- 

 ising out of the dispute about their origin, Tlie gen^ 

 eric name Lava^ simplifies the nomenclature adapted 

 by the Volcanists, w hile the Neptunians admitting of 

 few lavas, except those ejected from volcanoes at pre- 

 sent in action, have been forced to give other name« 

 to the great variety of rocks produced by volcanoes 

 now extinct;, or united by strong analogy to thesamq 

 ©rigin. 



