Mr. LyelVs Address. 399 



aflford proofs of modern clianjres in the level of the land, both of 

 upheaval and depression. The raised beach of Hope's Nose, 

 correctly described by Mr. Austen, is the most striking instance 

 in South Devon. 



The quantity of rise of land in the modern period is from ten to 

 forty feet in South Devon and Cornwall, nearly seventy feet in 

 North Devon, while in Lancashire, Cheshire, and Shropshire there 

 are marine deposits with recent shells at the height of from SOO to 

 500 feet above the sea. 



It is natural to inquire what changes the surface of the dry 

 land in England may have undergone during the occurrence of such 

 upward and downward movements. Perhaps some observations 

 lately made by Mr. Bowerbank in the south of the Isle of Wight 

 may elucidate this point. He has given us an account of a bed of 

 chalky detritus, containing recent land shells, (at Gore Cliff. This 

 bed is ten feet thick, and rests immediately upon chalk marl. 

 Many of the shells, which are plentifully scattered through it, retain 

 their colour. As the deposit ranges to the foot of St. Catherine's 

 Down, it is possible that the waste and denudation of that chalk 

 hill may have supplied the materials. I have lately seen similar 

 detritus resting on the chalk with flints, and arranged in numerous 

 thin layers in the section exposed in cutting the railroad at Win- 

 chester, where a black layer of peaty earth and carbonized wood 

 intersects thin layers of white chalk rubble, from twenty to thirty 

 feet thick. Such appearances are, in fact, very general in chalk 

 districts ; a bed of flints not waterworn occurring on the highest 

 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 



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



