30 GEOLOGICAL AGE AND FORMATION. 



tion includes those materials — sand, clay, gravel, and loose 

 stone — which have been brought to their present places 

 from sources more or less distant; while the Alluvial For- 

 mation includes those sands, clays, loams, mud, peat, &c., 

 which have been deposited where they now are, from 

 sources comparatively near. 



Of these two formations, the Drift is the oldest. The 

 mode of its origin, and the causes which have brought 

 its materials to their present places, have been the subject 

 of much discussion, and are not yet well understood. The 

 Alluvium is still forming, and the modes of its production 

 are various, but well known. 



§ The remains of animals and plants which are found 

 in the Alluvium are those of species still in existence; 

 and the same is true, of at least a part, of those of the 

 Drift. 



The Drift Formation, in this county, includes very nearly 

 all the uplands within its bounds. That part where loose 

 stones and boulders are found, is unquestionably of this 

 formation ; and the remainder of the upland, which con- 

 tains no fossils, which has extensive beds of gravel — the 

 gravel containing fragments of rocks which are in place 

 considerably north or northwest of this — and, in general, 

 which possesses none of those peculiar and distinctive cha- 

 racters belonging to the upland of the succeeding forma- 

 tion, is, so far as my present knowledge extends, properly 

 classed here. 



The Alluvium includes some limited portions of upland 

 not comprehended in the above description of the Drift. 

 It is not easy to draw a distinct line of division between 



