GEOLOGY. 



77 



without the risk of incurring much inaccuracy. It is not 

 designed in this treatise to give a full classification of all the 

 rocks, with a detailed description of their characters, but only 

 the outlines of classification, and a brief description of such as 

 are deemed most important to our present purpose. 



Notwithstanding the apparent discrepancies among the 

 systems of classification, " in all the essential principles, geolo- 

 gists are nearly agreed : they all admit one class to be stratified 

 and another unstratified: one portion of the stratified rocks 

 to be fossiliferous and another portion not fossiliferous : and 

 they generally agree also as to the extent of the different 

 distinct formations. Now these three principles are all that 

 are essential for classification ; and some of the best geologists 

 limit themselves to these." [Hitchcock.] 



One very common and natural classification of rocks is, into 

 two great families, viz : stratified and unstratified. We shall 

 give the outlines of two others, viz : the improved Wernerian 

 and that of Mr. Lyell. 



IMPROVED WERNERIAN CLASSIFICATION. 



( Alluvium, 

 ALLUVIAL. 



TERTIARY. <J Tertiary strata. 



ChalTc, 



Green sand, 



Wealden, 



Oolitic system, 



Lias, 



New red sandstone, 



Coal formation, 



Carboniferous limestone, 



Old red sandstone. 



SECONDARY. 



TEANSIT.ON. 



Silurian system, 

 ywt 



*7 



