Changes in Geography and Climate. 45 
deep freezing. This led to enormous and rapid denudation, 
over areas where the rain now sinks in and is slowly given 
out as springs. Masses of loose flint and chalk débris were 
swept off the South Downs and spread out in a wide sheet 
extending several miles over the lowlands, and over the 
Interglacial deposits already described. Even in Cornwall 
the rubbly drift known as ‘head’ seems to have marked a 
similar stage. It is difficult to believe that anything but a 
poor Arctic vegetation could have withstood these condi- 
tions, and the Arctic plants of Devon may belong to this 
cold epoch, rather than to the older one represented by the 
erratics of Sussex and the Boulder Clay near London. 
The Arctic mammals found near Salisbury may belong to 
the same stage, they are migratory or else Steppe species. 
The stage that follows—the transition from the 
Paleolithic to the Neolithic —is unfortunately one of the 
most obscure, and I can only suggest that the break is 
more apparent than real, and that one follows the other in 
close succession. No doubt there is generally a marked 
difference between deposits of Paleolithic and those of 
Neolithic age, the older series occupying terraces far above 
the reach of any flood, while the more recent series lie in 
the bottoms, or below the bottoms, of existing valleys. It 
may prove, however, that the climatic change and the 
difference in the position of the deposits are related as cause 
and effect, little change having really occurred in the 
contours of the country. As soon as the climate amelio- 
rated, frozen soil would no longer cause erosion and 
deposition to act in the peculiar way above described. 
The older deposits would be left stranded at all elevations, 
and denudation and deposition would at once change to 
the ordinary types caused by river action in a Temperate 
climate. With the climate, the fauna and flora would also 
change; and at the same time the race of hunters would 
