636 ISLAND LIFE 



of temperature between summer and winter ; but, wherever 

 there was a considerable extent of very lofty mountains 

 the snow-line would be lowered, and the snow-collecting area 

 being thus largely increased a considerable amount of 

 local glaciation might result. Thus may be explained the 

 presence of enormous ice-borne rocks in Eocene and 

 Miocene times in Central Europe, while at the very same 

 period all the surrounding country enjoyed a tropical or 

 sub-tropical climate. 



The general conclusion is thus reached, that geogTaphical 

 conditions are the essential causes of great changes of 

 climate, and that the radically different distribution of 

 land and sea in the northern and southern hemispheres 

 has generally led to great diversity of climate in the 

 Arctic and Antarctic regions. The form and arrangement 

 of the continents is shown to be such as to favour the 

 transfer of warm oceanic currents to the north far in 

 excess of those which move towards the south, and 

 whenever these currents had free passage thovugji the 

 northern land-masses to the polar area, a mild climate 

 must have prevailed over the whole northern hemisphere. 

 It is only in very recent times that the great northern 

 continents have become so completely consolidated as 

 they now are, thus shutting out the warm water from 

 their interiors, and rendering possible a wide-spread and 

 intense glacial epoch. But this great climatal change was 

 actually brought about by the high excentricity which 

 occurred about 200,000 years ago ; and it is doubtful if a 

 similar glaciation in equally low latitudes could be produced 

 by means of any such geographical combinations as 

 actually occur, without the concurrence of a high excen- 

 tricity. 



A survey of the present condition of the earth supports 

 this view, for though we have enormous mountain ranges 

 in every latitude, there is no glaciated country south of 

 Greenland in N. Lat. 61°. But directly we go back a 

 very short period, we find the superficial evidences of 

 glaciation to an enormous extent over three-fourths of the 

 globe. In the Alps and Pyrenees, in the British Isles 

 and Scandinavia, in Spain and the Atlas, in the Caucasus 



