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. 
