VARIATION IN THEIR POWER 29 



The bones are dispersed irregularly throughout the 

 mass of rubble, but the land shells are confined to the 

 finer beds. Fragments of wood are only occasionally 

 met with. Decay, however, has generally destroyed 

 all the vegetable matter. 



These considerations, added to the circumstance 

 that this rubble contains the remains of a land fauna 

 only, led me to infer that the South of England had 

 been submerged at the close of the Post-glacial 

 period to the depth of not less than about 1,000 

 feet, for to that height there are traces of this 

 Kubble-drift. As the surface of the submerged area 

 shows no marine terraces indicating periods of rest, 

 it may be inferred that the submergence was com- 

 paratively slow and gradual, the only disturbance 

 being the removal of the finer surface materials and 

 sediment, with which the waters would become 

 charged. On the other hand, the alternation of fine 

 and coarse materials in the Head indicate that the 

 upheaval was by movements alternately slow and 

 rapid, during the latter of which the debris of the 

 surface so submerged was swept down to lower 

 levels, or lodged in the hollows and fissures of 

 that surface, together with the remains of the 

 animals and land shells that had inhabited the 

 submerged land. I conclude, further, from the 

 absence of marine sedimentation and of marine 

 shells on the submerged area, that the submergence 

 was of too short duration to admit of such sedimen- 

 tation, or to afford time for the immigration of a 

 marine fauna from adjacent iinsubmerged areas. 



