REPLY TO CRITICS. 53 



go on rapidly, and by the end of the summer the snow 

 would all disappear except on high mountain-summits 

 such as those of Scotland, Wales, and Scandinavia. 

 Before the end of autumn, however, it would again 

 begin to fall. Xext year would bring a repetition of 

 the same process, with this difference, however, that 

 the snow-line would descend to a lower level than in 

 the previous year. Year by year the snow-line would 

 continue to descend till all the high grounds became 

 covered with permanent snow. 



It would not require a very great amount of change 

 from the present condition of things to bring about 

 such a result. A simple lowering of the temperature, 

 which would secure that snow, instead of rain, should 

 fall for six or eight months in the year, would suffice ; 

 and this would follow as a necessary result from an 

 increase of eccentricity. Xow, if all our mountain- 

 summits were covered with permanent snow down to 

 a considerable distance, the valleys would soon become 

 filled with local glaciers. In such a case we should 

 then have more than one-half of Scotland, a large part 

 of the north of England and Wales, with nearly the 

 whole of Xorway, covered with snow and ice. Here a 

 new and powerful agent would come into operation 

 which would oreatlv hasten on a o-lacial condition of 

 thino-s. This laro-e snow-and-ice-covered surface would 

 tend to condense the vapour into snow. It would, 

 during summer, chill the air and produce dense and 

 continued fogs, cutting off the sun's rays, and leading to 

 a state of things approaching to that of South Georgia, 

 which would much retard the melting of the snow. 



It is a great mistake, as I have repeatedly shown, 

 to suppose that the perihelion summers of the glacial 

 epoch could be hot. No snow-and-ice-covered continent 

 can enjoy a hot summer. This is clearly shown by the 



