PRELIMINARY CONSIDERATIONS. 67 



height of the snow-line, tend to show that a general 

 decrease of temperature to the extent of from 4-5 

 degrees Centigrade (all other atmospheric conditions 

 remaining the same as now) would be sufficient to 

 give us back the Glacial period. 



Professor Neumayr (p. 619) adopted a similar prin- 

 ciple in determining the temperature which prevailed 

 in Europe during the Glacial period. Snow now lies 

 in the Pyrenees 1000 metres higher 'than it did then, 

 1,200 metres higher in the Alps, and 800 metres 

 higher in the Tatra mountains. Since the tempera- 

 ture in Central Europe decreases by half a degree 

 Centigrade for every 100 metres of elevation, it follows 

 that if the glacial phenomena had only been brought 

 about by a decrease of temperature without an in- 

 crease of moisture, we should have had a reduction 

 of temperature during the Glacial period of six 

 degrees Centigrade in the Pyrenees, of seven degrees 

 in the Alps, and of four in the Tatra mountains. 

 The general lowering of the temperature of Europe, 

 says Professor Neumayr, could not have amounted to 

 more than six degrees Centigrade. Moreover, he is 

 of opinion that the very low snow-line in the British 

 Islands proves that even during the Ice Age a com- 

 paratively mild climate prevailed there, and that 

 the climatic conditions generally, in the different 

 parts of Europe, were relatively about the same as 

 they are now. 



Professor J. Geikie does not give us his views as to 

 the temperature of the Glacial period, but he main- 



