154 Sketch of a Classification 



gravels, clays, &c. formed previously to the existing order of 

 things. There are indeed a few exceptions to this observa- 

 tion, but the body of evidence seems to render a new creation 

 presumable. 



Group 2. (Diluvial) comprises those gravels so commonly 

 occurring in situations where actual causes could not have 

 placed them, but where, on the contrary, such causes tend to 

 destroy them. The most extraordinary feature of thi3 group 

 is the distribution of those enormous blocks or boulders found 

 so singularly perched on mountains, or scattered over plains 

 far distant from the rocks from whence they appear to have 

 been broken. Many valleys appear to have been scooped out 

 of horizontal or nearly horizontal strata at this epoch; the 

 force which excavated them having acted often upon strata 

 shattered and broken into faults. Of course a general modifi- 

 cation of the previously existing forms of mountain and valley 

 must have taken place, if we are to consider the catastrophe 

 general. Much information is yet wanting respecting this 

 group, which it is hoped those observers who have been more 

 especially occupied with it, will soon afford us. 



Group 3. (Lowest Great Mammiferous) comprises the rocks 

 commonly known as tertiary: they are exceedingly various, 

 and contain an immense accumulation of organic remains, 

 terrestrial, fresh-water, and marine. The recent observations 

 of some able geologists have shown, that the upper members 

 of this group approach more closely than was formerly sup- 

 posed to the existing order of things. We yet require much 

 information respecting even the European rocks composing 

 this class, notwithstanding the labours of those who may 

 almost be said to have devoted their exclusive attention to 

 them. The group is characterized by the first appearance, in 

 the ascending series, of any abundance of the mammiferous 

 animals, many genera of which are now extinct. 



Group 4. (Cretaceous) contains the rocks which in England 

 and the North of France are characterized by chalk in the 

 upper part, and sands and sandstones in the lower. The terra 

 " cretaceous" is perhaps an indifferent one; for, possibly, the 

 mineralogical character of the upper portion whence the name 

 is derived is local, that is, confined to a particular portion of 

 Europe, and may be represented elsewhere by dark compact 

 limestones or even sandstones. As however the geologists of 

 the present day are perfectly agreed as to what rock is meant 

 when we speak of " the chalk," there seems no objection to 

 retain it for the present. The French geologists have long 

 considered the sands beneath the chalk, known as green-sands, 

 as belonging to the same formation with the chalk. That the 

 fresh-water character of the shells contained in the Wealden 

 rocks is more or less local it seems but rational to infer ; for 



