226 NEOZOIC TIME. [CHAP. XI. 



there were, in the upper parts of the river, lakes such as 

 those of Bovey Tracey, which intercepted drifting timber ; 

 its abundance in other beds marking the time when these 

 had been filled in." After the completion of the geo- 

 graphical changes which took place during the formation 

 of the Lower Bagshot Beds, it is evident that the whole 

 area underwent a gradual subsidence which allowed the 

 sea to regain a part of its lost domain. To quote again from 

 Mr. Gardner : " In the Bournemouth Beds we have deposits 

 of the same river, but in a more open and level valley, and in 

 closer proximity to the sea. In all the lower or freshwater 

 series we have no sign of the presence of sea water, and 

 when we do find it in the higher beds to the east, it is not 

 that the river deposits encroached there on the sea, but 

 that the land gradually sank, and allowed the sea to cover 

 them." 



" It is of great interest to trace through these beds the 

 change from a comparatively upland flora to a valley, and 

 then to a swamp flora ; to follow out the lowering of the 

 land until it became sea ; to trace the sea, first trickling in, 

 as it were, and forming lagoons, then overwhelming the 

 mud deposits formed by these lagoons, with shingle and 

 sand ; to realize, in fact, the actual shore-line, now marked 

 by river deposits, full of plant remains on one side, and a 

 sea fauna with sharks' teeth on the other. 



" The series of marine beds from Bournemouth to High- 

 cliff, which belong to the Bracklesham Beds, are the shore 

 deposits of the southern sea. The Bracklesham series 

 proper show a gradually deepening sea ; for, while the beds 

 of sand which are prevalent in the lower stages show 

 shallow water, the clay beds above them were formed in a 

 deeper sea, and contain deeper water mollusca. In compar- 

 ing the marine fauna with that of the London Clay, its very 

 much more tropical character is apparent. Many southern 

 types of mollusca abound in it which are scarcely repre- 



