12 INFLUENCE OP CLIMATIC AND GEOLOGICAL CHANGES 



distribution of British plants, on account of a break in the series of 

 the Tertiary strata. The Middle Tertiary Flora can be favourably 

 studied in the Oligocenes of Hampshire ; it is sub-tropical, and 

 allied to our present-day flora. During the succeeding Miocene 

 Period there appears to have been a period of earth-movement, 

 when the surface configuration of Great Britain was completely 

 changed. During the subsequent Pliocene Period there is 

 evidence of a slow refrigeration which culminated in the Glacial 

 Age. The strata of the older Pliocenes in Great Britain as 

 yet discovered are marine and laid down in a warm sea. It is 

 only in the later deposits we find a copious land fauna and flora. 

 The history of the plants now inhabiting Britain commences 

 with the Cromer Forest-bed, consisting of a series of estuarine 

 and lacustrine strata. At that period the Straits of Dover had 

 not been cut through, England \vas then connected with Belgium 

 and Holland by a wide alluvial plain. Dewlish, in this county, 

 has yielded bones of the Pliocene Elephant, Elephas meridionalis. 

 Owing to the close proximity of the deposit to the surface the 

 larger bones, such as the femur, humerus, scapula, pelvics, tusks 

 and molars only are preserved ; all the rest have been entirely 

 obliterated by atmospheric agencies, which will account for the 

 absence of any evidence of the contemporary fauna and flora. 

 The age of this deposit is earlier than that of the Forest-bed, and 

 when the climate was much warmer. The plants and animals of 

 the Forest-bed indicate a climate similar to that of the present 

 day. The presence of Najas marina in the Forest-bed suggests 

 that this plant is a survival, and was not exterminated by the ice, 

 and then re-migrated from its new home back to one spot in 

 Norfolk only, . in Hickling Broad. Although the Lusitanian 

 group in Ireland is represented by only a few species, they play 

 an important part in the vegetation of that region, and are all 

 found in the Spanish Peninsula, notably in the Asturias. A great 

 number of the species belonging to the South-Western British 

 flora appear to have originated in South-Westcrn Europe, or 

 at least to have spread over our Islands from that quarter ; their 

 home was probably in a warm, damp climate. At the time of 



