CHAP. XI.] HANTONIA.N PERIOD. 217 



watered by a copious rainfall ; the contents of the gravel 

 beds prove that rapid erosion was in progress ; while the 

 plant remains show that the lower slopes of the volcanoes 

 and of the surrounding land were clothed with an abun- 

 dant vegetation. We must, therefore, picture a country in 

 which all the terrestrial agents of change were in full 

 activity, a country where fire and water frequently con- 

 tended for the mastery, where wide districts were from 

 time to time devastated by burning streams of lava, but 

 were soon restored to fertility by cooling showers and by 

 the irrigation of a thousand streams that sprang from 

 the slopes of cloud-capped mountains. 



Coming now to the area within which sedimentation 

 was taking place, it is evident from a comparison of the 

 English and Belgian strata that Belgium came within the 

 influence of the Eocene sea before England did, and that 

 a depressive movement allowed the sea to advance westward 

 and to occupy portions of Kent, Surrey, Essex, and Suffolk, 

 at the time of the Thanet Sands. The area which these 

 sands seem originally to have covered is indicated in 

 Plate XI. by the finer blue lines, and this tract appears to 

 have been part of a large bay which extended from the 

 northern sea into the Anglo-French land region. 



From the nature of the beds in East Kent the abun- 

 dance of glauconite grains, the admixture of calcareous 

 matter, and the presence of such shells as Pholadomya 

 we may infer that the sea was moderately deep in that 

 district; while the replacement of these beds by sharp 

 quartzitic sands to the westward proves the water to have 

 become shallower in that direction. From the purely 

 marine character of the beds we may conclude that the 

 sediment was carried by marine currents circulating round 

 the bay in the same manner as such currents now circu- 

 late in the North Sea. From the absence of pebble beds 

 we are justified in supposing the shores to have been low, 



