130 Ou the Mammalian Drift of Wiltshire and its Fossil contents. 



with any historic period, immeasurably remote. The Post-Tertiary 

 deposits of England are much more extensive than they were 

 formerly supposed to be, and comprise several distinct sets of 

 superficial strata. Their relative age has not yet been satisfactorily 

 determined, but the beds which we have more especially to describe 

 are considered by Sir Charles Lyell to be of the same age as that 

 great sheet of ochreous gravel which is spread out over" the valley 

 of the Thames, (above the deposits of Grays and Ilford,) and which 

 extends eastward from above Maidenhead, through London, to the 

 sea, a distance of 50 miles.^ Before going into any detailed account 

 of the Animals of this period, I will endeavour to give a general 

 idea of the Drift itself, and more particularly as we find it in our 

 own county. 



This gravelly deposit is composed of the broken up fragments 

 of the subjacent strata, mixed with flint, sand, and clay, and contain- 

 ing layers of pebbles, which have been rolled and bouldered by the 

 action of water out of their parent rock. It does not contain a 

 single admixture of any far- transported fragments; and there is 

 abundant evidence to prove that the deposit was gradual, occupying 

 a long period of time. 



This Drift is not only to be found scattered at intervals over the 

 valleys of England, Scotland, and Ireland, but also all over the 

 northern pai'ts of Europe and Asia, and the river plains of North 

 America ; presenting every where the same features, and containing 

 similar organic remains. In our own county — in the broad and 

 fertile valley of the Avon, from Tetbury, passing by Malmsbury, 

 Christian !Malford, Kellowaj's, Chippenham, Lacock, Melksham, 

 Broughton, Bradford, and so on to Bath — and in the narrow valleys 

 that intersect our wide and undulating do^Tis, such as the valley of 

 the Wiley, of the Nadder, and of the River Bourn, we have repeated 

 and instructive examples of the Drift.'^ 



It varies in thickness from 5 to 30 feet, and in many places con- 

 tains the bones and teeth of gigantic, extinct, land Animals, such 



1 Lyell's Supplement to the oth edition of Manual of Geology, 1857. 

 2 In the Map of Wiltshire coloured hj' the Ordnance Survey, and puhlished 

 ^.ij? vear (1857), these valleys are distinguished by a light yellow tint. 



