152 



INTRODUCTION TO PLANT GEOGRAPHY 



[chap. 



deposits they often extend far (and in post-Pleistocene ones sometimes 

 considerably) beyond their present limits, suggesting substantial 

 changes in climate since they were laid down. Indeed, such changes 

 we know to have taken place in the northern parts of Eurasia and 



Fig. 41. — A reconstructed scene in Switzerland during 

 Miocene times (after Heer). 



America, where several periods of advancing and declining glaciation 

 widely affected the climate, and where further changes are indicated 

 by such evidence as that afforded by sub-fossil pollens and other 

 remains of contemporary plants preserved in bogs. These remains, 



