298 THE BEDSHIEL KAIMS 



must not be left out of account. Indeed, it is often the per- 

 sistent action of these minor causes of change that determines, 

 in the long run, whether the climate of large regions shall 

 be humid or arid, temperate or arctic. Latitude has already 

 been referred to as one of the factors of major importance. 



Next in importance to that comes elevation above the 

 sea, for it is usually altitude that determines whether the 

 precipitation shall take the form of rain or that of snow. 

 Position in relation to prevalent winds blowing fi'om a 

 large extent of water, or from a large extent of land, is 

 also important. The results arising from these conditions, 

 variously combined, are capable of very materially modifying 

 the effects produced by the direct action of the Sun. To 

 realise the effects of elevation, we have but to consider what 

 happens nearly every year on Ben Nevis, or occasionally on 

 hills as low as the Cheviots. It is often the case that snow 

 lingers in sheltered spots near the summits of these mountains 

 from one year's end to another. If these hills were only 

 a few hundred feet higher, much larger quantities of snow 

 would fall, and much more would be left. It is perhaps 

 well to remark, in this connection, that intensity, or the 

 reverse, of sunheat is not the sole determining factor in 

 such cases. More sunheat reaches the summits of these 

 mountains than passes to the low ground. On the Alps 

 the difference between the sunheat on the mountain tops 

 and that in the bottom of the valleys is respectively as 6 

 to 5 ; so it is obvious that the presence of the snow is 

 determined partly by some other cause than what is com- 

 monly supposed. 



Now, to show why the next set of facts is presented for 

 consideration, I may at once state in brief what the Glacial 

 Period really was. It was that recent episode in the 

 world's history when more snow fell on the lowlands of one 

 part than the summer's heat there could melt. In this 

 sense there is still a glacial period in Greenland, Labrador, 

 and the parts adjoining. There is also a glacial period in 

 the Antarctic regions. Furthermore, there must always have 

 been a glacial period at some part of the earth's surface or 

 other, from the dawn of geological history down to the 

 present day. All that happens in each case is that, from 



