284 EOCENE PERIOD. [Ch. XX. 



those spaces where the outliers above mentioned occur, nor 

 that the comparative thinness of those deposits in the higher 

 chalk countries should be attributed chiefly to the greater 

 degree of denudation which they have there suffered. 



Origin of the English tertiary strata. In explanation of 

 the phenomena above described, we shall endeavour, in the two 

 next chapters, to lay before the reader a view of the series of 

 events which may have produced the leading geological and 

 geographical features of the south-east of England. 



A preliminary outline of these views may be useful in this 

 place. We conceive that the chalk, together with many sub- 

 jacent rocks, may have remained undisturbed and in horizontal 

 stratification until after the commencement of the Eocene period. 

 When at length the chalk was upheaved and exposed to the 

 action of the waves and currents, it was rent and shattered, so 

 that the subjacent secondary strata were exposed at the same 

 time to denudation. The waste of these rocks, composed chiefly 

 of sandstone and clay, supplied materials for the tertiary sands 

 and clays, while the chalk was the source of flinty shingle, and 

 of the calcareous matter which we find intermixed with the 

 Eocene clays. The tracts now separating the basins of London 

 and Hampshire were those first elevated, and which contri- 

 buted by their gradual decay to the production of the newer 

 strata. These last were accumulated in deep submarine 

 hollows, formed probably by the subsidence of certain parts of 

 the chalk, which sank while the adjoining tracts were rising. 



