34 Origin of the B7dtish Flora. 



persal of the species, and a short discussion of the principal 

 changes that can be shown to have taken place may assist 

 in explaining some of the anomalies in geographical 

 distribution. 



It is useless for our present purpose to go back to any 

 distant geological period, for in Britain there exists so vast 

 a break in the series of Tertiary strata that we are unable 

 to bridge it. Our Middle Tertiary flora, which can be 

 studied in the Oligocene strata of Hampshire, is a sub- 

 tropical one, not allied to that now occupying the country. 

 The history of the succeeding Miocene Period in these 

 islands is a complete blank, for we have no fossiliferous 

 deposits of that age, and all we can say is, that the 

 Miocene appears to have been a period of great earth- 

 movement and folding, under which the surface con- 

 figuration of Britain was completely changed. Whether 

 Britain was then under water or was mainly dry land we 

 do not know. Certain of the Miocene plants found on 

 the Continent are living European species — probably none 

 of them now British — and the flora as a whole begins to 

 show a distinct affinity with that now occupying the 

 southern parts of the Continent. 



Throughout the Pliocene Period there is evidence of 

 the slow refrigeration which culminated in the Glacial 

 Epoch ; but unfortunately, as far as the botany is con- 

 cerned, this climatic change cannot be followed, for plants 

 only occur in the newest stage of the period. The whole 

 of the strata of Older Pliocene age yet discovered in Britain 

 are of marine origin, and were laid down at some distance 

 from land in a warm sea. The Coralline Crag of Suffolk 

 yields, however, a few drifted land-shells, and at its base 

 contains bones of land animals, washed out of some older 

 deposit ; but there are in it no determinable plant-remains. 

 A few pieces of much decayed worm-eaten drift-wood are 



