276 A Geological Sketch of the Valley of the Kennet. 



shape by supposing that it acquired its roundness through long 

 continued friction on the shores of some surging sea. Still more 

 incongruous are the fossils imbedded in the gravel. Echini, sponges, 

 and other organic remains peculiar to the chalk, all of which belong 

 to species which were extinct before the tertiary beds were de- 

 posited, are found side by side with remains of families which had 

 no existence until the close of the tertiary era. Whence came all 

 those discordant materials, and by what agency were they conveyed 

 hither? Are we to ascribe their strange conjunction to the action 

 of ice, river, or sea ? And what relation in point of age do the 

 gravel beds themselves bear to the strata on which they rest ? 

 These are questions which cannot with our present data be satis- 

 factorily answered ; but the process by which those beds were in 

 all probability laid down, may without much difficulty be traced. 

 After the deposition of the Bagshot sands, an upheaval of the land 

 took place, gradually no doubt, and imperceptibly to the creatures 

 that inhabited the district, until the ocean bed over which the 

 Bagshot sands had been spread, became first a swampy waste, and 

 afterwards dry ground. Then ages rolled on, during which the 

 raw material, so to speak, of our gravel beds was prepared by the 

 wearing down of the soft chalk by rains and atmospheric influences. 

 Meanwhile tremendous mutations were taking place in other 

 regions of the globe. The Continent of central Europe, e.g., was 

 emerging from the sea, and the Alps, whose highest peaks had 

 been islands, were gradually rising into a stupenduous chain of 

 mountains. This elevation of the land, acting as it did more or 

 less over the whole northern hemisphere, could not fail to alter 

 the climate of this country, and to modify many of the conditions 

 of its animal and vegetible life. Perhaps the ocean currents too, 

 which like our present gulf stream had for a great lapse of time 

 given a genial warmth to those shores, were diverted from their 

 old course by changes in the relationship of land and sea ; thereby 

 tending still more to lower the temperature of the climate. Hence 

 the sub-tropical forms of life which had flourished here during the 

 tertiary epoch, soon began to disappear. Palm trees and other 

 products of the sunny south, gave place to pine forests and such 



