816 THE AGE OF SOME EXISTING SPECIES OF PLANTS. 
myrtilloides L. and §. polaris Wahl.; and Betula nana L. has 
retreated to the mountains of Scotland. Three others (Dryas 
octopetala L., Arctostaphylos Uva-ursi L., and Salix herbacea Li) have 
withdrawn to the mountains of Northern E gland, , and 
Scotland, while the remainder are still found scattered over the 
country. Notwithstanding the diverse physical conditions to which 
these plants have been subjected, the remains preserved in these 
beds present no characters by which they can be distinguished 
from the living representatives of the species. 
meet with no further materials for careful comparison with 
i nse 
these alterations of temperature, extensive changes in the 
— of the land were taking place. The first great 
CAV: . * . 
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250,000 years, estimating the time of the first of ar as 200,000 
years ago, while the subsidence took place 50,000 years later, and 
the second upheaval 92,000 years ago. 
The sedimentary deposits later than the Pliocene strata, but 
— older than the glacial drift, indicate an increasing severity in the — 
ae climate, which reached its height in the first glacial period. : 
es At Cromer, on the Norfolk coast, the newest of these deposits 
