52 FORMATION OF THE EARTH 



silver-fir, and water-lilies flourished there. In Greenland, 

 in lat. 70 , magnolias flourished. A little later, during the 

 Oligocene Period, in the area corresponding to our present 

 temperate regions, there was now a mixed flora, now a 

 localization of temperate flora and tropical flora, indicating 

 that the vegetation had come under the influence of the 

 temperature of the coastal currents. On the other hand, the 

 nature of the arctic flora in the Neogene Period points to a very 

 definite increase of cold in these regions. It was in this period 

 that the largest of our existing mountain chains was formed, 

 and, as in the case of the formation of the Caledonian and 

 Hercynian chains, glaciers soon made their appearance. 



The plants of the warm climates gradually moved south and 

 were replaced by trees with caducous foliage, bearing witness 

 to an alternation of cold and warm seasons. The camphor- 

 tree, however, still flourished at a latitude of 51 , and palms 

 at 50 ; the flora was identical from lat. 38 to lat. 54 — from 

 Serbia to Finland. 



By the time that the Alpine-Himalayan chain had attained 

 a great altitude the Oligocene epoch was in full sway. The 

 presence of these large massifs conduced to condensation, and 

 the summer became rainy ; but the winter still remained 

 warm. Along the shores of Lake Constance there was a climate 

 like that of Madeira and the south of Japan ; the mean 

 temperature of the shores of the Sea of Okhotsk was about 

 19 . But a period of erosion and settling followed for the new 

 mountain chains. Torrential rains, caused by their very 

 height, ravaged their slopes, cutting deep valleys, and there was 

 a tremendous extension of glaciers. 



This brings us to the beginning of the Quaternary Period, 

 which witnessed man's conquest of the soil. During this 

 period, apart from the changes in land elevation due to the 

 formation of mountain chains, it seems that extensive 

 continental areas experienced alternate elevation and settling 

 movements constituting what are known as epirogenic 

 movements. During the periods of upraising, the glaciers that 

 had formed in the valleys of the high ranges extended very far, 

 only to retreat again during the epochs of settling. The climate 

 naturally became colder in the neighbourhood of the glaciers, 

 but in regions distant from them it still remained mild. 



