458 PLEISTOCENE DEPOSITS. CHAP. 



of these hill gravels are often found in low ground mixed with 

 those in the true valley deposits, under circumstances which 

 indicate the anterior date of the former. They have indeed often 

 been swept down from their original sites on higher ground by 

 rains and rivers, at some later time than the epoch of their arrival 

 in the drainage of the Thames, 



These hill gravels are composed of materials which it is im- 

 possible to suppose to have been drifted at any time or under any 

 circumstances by water flowing as a river or inundation from 

 atmospheric precipitations ; the extent of ground occupied, and the 

 nature of the pebbles and fragments, imply the agency of wide 

 ocean streams, mostly directed from the northward to the south- 

 ward. A marine origin is thus found for the hill gravels, but I 

 am not aware of any modern reliquiae of the sea being found in 

 them within the drainage of the Thames, though ancient fossils 

 are common enough among them in particular places. Floating 

 ice has been suggested as the vehicle of the transport of these 

 extra-Tamisian stones, and their geological date is expressed by 

 the term 'glacial/ the valley gravels being universally admitted 

 to be ' post-glacial/ 



Flint implements memorials of more than one early period of 

 imperfect British civilization have been found in the Thames 

 Valley at several points in descending its course from Dorchester 

 near Oxford to Reculver. Up to the present time they have not 

 been discovered in the hill gravels, and only at small depths in 

 or at the surface of the valley gravels. 



Kemains of mammalia occur in the valley gravel, silt, and peat ; 

 some of species long since extinct in these regions, as the mam- 

 moth and rhinoceros (both when alive covered with hair and 

 wool), hippopotamus and bear; others formerly resident, as the 

 beaver, roe-deer, red-deer, goat, and wolf; and others still feed- 

 ing in our pastures and subject to domesticity, as the horse and 

 the ox. 



HILL OR HIGH LEVEL GEAVEL. 



On a large portion of the Cotswolds, but not rising to their 

 greater elevations, we find a scattered gravel deposit, of a kind 

 entirely different from that which is so common in the greater 



