504 



downs, while fragmentary chalk, often inclosing land shells, occurs 

 on their slopes and at lower levels. Violent rains have been known 

 even of late years to tear off the turfy covering from certain points 

 near Lewes, and to wash away flints and chalky mud, and leave 

 them in the hollow combs or flanks of the hills. This action of the 

 elements would be most powerful at periods when the chalk first 

 emerged from the sea, or whenever it assumed in the course of sub- 

 terranean disturbances a new position or physical outline. 



We must, I think, infer from the occurrence of certain recent 

 marine shells and shingle in the bottom of what has been termed 

 the elephant-bed at Brighton, that the chalk in the South-east of 

 England has undergone some movements of a modern date, the 

 land having subsided there to the depth of fifty or sixty feet, and 

 having been subsequently raised up again to a level somewhat 

 higher than its original position*. 



If it should appear upon careful research that the land shells found 

 in terrestrial alluviums covering the chalk are almost universally 

 of recent species, I should not conclude that the emergence of the 

 chalk hills from the sea had generally occurred at a very modern 

 period, but merely that these hills had been modified in shape in 

 recent times, and that during that modification alluviums of older 

 date had been washed away, or the land shells which they may once 

 have contained have decomposed and disappeared. In regard to 

 the great numbers of these shells preserved throughout the bed at 

 Gore Cliff, and in many other places even at greater depths, it will 

 not seem surprising to those who have observed the number of dead 

 land shells which are strewed over the surface of the chalk downs, 

 or lie concealed in the green turf in numbers almost as countless as 

 the blades of grass. If the slightest wash of water should pass 

 over such a soil, it must float off myriads of these shells, and they 

 would immediately be involved in that white cream-coloured mud 

 which descends from wasting hills of chalk after heavy rains. Land 

 shells so buried may retain their colour for indefinite periods, as is 

 shown by the state of species in the loess of the Rhine, and even in 

 tertiary strata of much higher antiquity. 



While a variety of geological monuments are annually discovered 



* See Principles of Geology, 4th edit,, vol. iv. p. 274. 



