170 ANCIENT PLANTS 



under known conditions, and judge of the climate that 

 had nurtured the fossil plant while it grew. 



Previous to the present period there was what is so 

 well known as the Glacial epoch. In the earthy deposits 

 of this age in which fossils are found plants are not un- 

 common. They are of the same kind as those now 

 growing in the cold regions of the Arctic circle, and on 

 the heights of hills whose temperature is much lower 

 than that of the surrounding lowlands. Glacial epochs 

 occurred in other parts of the world at different times; 

 for example, in South Africa, in the Permo-Carboniferous 

 period, during which time the fossils indicate that the 

 warmth-loving plants were driven much farther north 

 than is now the case. 



It is largely from the nature of the plant fossils that 

 we know the climate of England at the time preceding 

 the Glacial epoch. Impressions of leaves and stems, 

 and even of fruits, are abundant from the various periods 

 of the Tertiary. Many of them were Angiosperms (see 

 Chap. VIII), and were of the families and even genera 

 which are now living, of which not a few belong to the 

 warm regions of the earth, and are subtropical. It is 

 generally assumed that the fossils related to, or identical 

 with, these plants must therefore have found in Tertiary 

 Northern Europe a much warmer climate than now 

 exists. Not only in Northern Europe, but right up 

 into the Arctic circle, such plants occur in Tertiary 

 rocks, and even if we had not their living representa- 

 tives with which to compare them, the large size and 

 thin texture of their leaves, their smoothness, and a 

 number of other characteristics would make it certain 

 that the climate was very much milder than it is at 

 present, though the value of some of the evidence has 

 been overestimated. 



From the Tertiary we are dependent chiefly on im- 

 pressions of fossils ; anatomical structure would doubtless 

 yield more details, but even as it is we have quite 

 enough evidence to throw much light on the physio- 



