of the European Rocks. 4f45 



tered and broken into fault&. Of course a general modifica- 

 tion of the previously existing forms of mountain and valley 

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

 treneral. 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 Mammiferoiis) comprises the rocks 

 commonly known as tertiary : they are exceedingly various, 

 and contain an immense accumulation of organic remains, ter- 

 restrial, 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 supposed 

 to the existing order of things. We yet require much infor- 

 mation 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 ascend- 

 ino- series, of any abundance of the mammifi^rous animals, 

 many genera of which are now extuict. 



Group 4. {Cretaceous) contains the rocks which in En- 

 gland and the North of France are characterized by chalk in 

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

 term " cretaceous" is perhaps an indifferent one ; for, pos- 

 sibly, 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 geo- 

 logists of the present day are perfectly agreed as to what rock 

 is meant when we speak of " the chalk," there seems no ob- 

 jection 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 it cannot be imagined that all the waters of the globe 

 became suddenly fresh in order that these rocks might be 

 formed, and as suddenly salt again for the deposition of the 

 green-sands and chalk. Some French geologists moreover 

 consider that in France there is a marine ecjuivalent of the 

 Wealden rocks. 



As far as our observations of fossil organic remains have 

 yet extended, it would seem probable that the ammonites and 

 belemnites ceased to exist after the fornuition of this group ; 

 for, as yet, tiieir remains have not been detected in Group 3. 

 Should this, alter a greater extent of the world has been ex- 

 amined, be found generally true, it will be a most valuable guide 



in 



