EuTLAND.— T/ic Fall of the Leaf. 115 



hitherto low-lying region clothed with evergreen vegetation, 

 and the consequent climatic changes, other causes beside the 

 mere lowering of temperature would assist in determining the 

 upland flora, and that amongst the species thus selected 

 those capable of assuming the deciduous habit might be only 

 in part included, or might be wholly omitted. 



We may now turn to the second class of climatic changes 

 to which portions of the earth have been subjected. Though 

 the causes which operated to bring about the cold of the 

 European glacial period are unknown, there is abundant 

 evidence that prior to its commencement that continent 

 enjoyed a climate as mild as, or milder than, at present prevails. 

 Whether during this pre-glacial epoch an evergreen vege- 

 tation clothed the plains and mountains cannot well be 

 determined, but the fact that Australian forms are found 

 amongst the fossil-plants of the Swiss miocene rocks at least 

 suggests that the flora of the northern and southern hemi- 

 spheres did not differ as widely then as now. 



Assuming that Europe at the close of the tertiary epoch 

 supported a vegetation similar to what is now found in cor- 

 responding southern latitudes — that evergreen trees, with a 

 small percentage of deciduous forms, then prevailed — let us 

 ask what would have been the effect of the coming-on and 

 subsequent passing-away of the glacial cold. 



Before approaching this question it may be well to review 

 what is known of the glacial period. That movements of 

 upheaval and subsidence on a considerable scale took place in 

 Europe during the continuance of the glacial cold is evidenced 

 by the deposits of the period and the present distribution of 

 animal life on the continent and adjacent islands. 



Thus, in the commencement of the period when the cold 

 was most intense, the continent extended westward of the 

 area now occupied by the Hebrides and Ireland, the land 

 being generally higher than the existing islands. 



Towards the middle of the period a movement of sub- 

 sidence commenced, and continued until only w^hat are now 

 the tops of the highest British mountains remained above 

 water, forming an arcliipelago of small islets, amongst which 

 drifted masses of floating ice, depositing where they grounded 

 quantities of debris, which still remain on the mountain-sides 

 in the form of stratified deposits, containing marine shells. 

 This movement of subsidence was followed by one of elevation 

 which brought the British Islands to their present level. As 

 the land rose, the cold, which had abated during the down- 

 ward movement, again increased, though not to what it had 

 previously been. Although the greatest cold of the glacial 

 period in Europe was coincident with the greatest elevation of 

 the land, we cannot in any way ascribe the great climatic 

 8 



