310 EOCENE PERIOD. [Qi, XXII. 



No. 81. 



water E, the sediment being drifted through transverse fissures, 

 as before explained. In this case, the rise of the formations 

 Nos. 1, 2, 3, 4, 5, may have been going on contemporaneously 

 with the excavation of the valleys C and D, and with the accu- 

 mulation of the strata a. There must be innumerable points 

 on our own coast where the sea is of great depth near to islands 

 and cliffs now exposed to rapid waste, and in all these the 

 denuding and reproductive processes must be going on in the 

 immediate proximity of each other. Such may have been the 

 case during the rise of the Valley of the Weald> and the 

 deposition of the beds of the London and Hampshire basins. 



The theory above proposed requires that the deposits a 

 should be composed, for the most part, of a mixture of such 

 mineral ingredients as would result from the degradation of 

 the secondary groups, Nos. 1, 2, 3, 4, 5. Now the tertiary 

 strata answer extremely well to these conditions. They con- 

 sist, as we have before seen, of alternations of variously-coloured 

 sands and clays, as do the secondary strata from the group 

 No. 5 to No. 2 inclusive, the principal difference being, that 

 the latter are more consolidated. 



If it be asked, where do we find the ruins of the white chalk 

 among our Eocene strata ? We reply, that the flint pebbles 

 which are associated in such immense abundance with the sands 

 of the plastic clay, are derived evidently from the destruction 

 of chalk ; and as to the soft white calcareous matrix, we may 

 suppose it to have been reduced easily to fine sediment, and to 

 have contributed, when in a state of perfect solution, to form 

 the shells of Eocene testacea; or when mixed with the waste of 

 the argillaceous groups, Nos. 2 and 4, which have been pecu- 

 liarly exposed to denudation, it may have entered into the 

 composition of the London clay, which contains no slight 



