260 Dr. J. Croll on some Controverted Points 
begin ; but it would be a very considerable time before the 
amount melted would equal the daily amount of .snow falling. 
Rain, alternating with snow-showers, would probably result ; 
and, for some time before midsummer, snow would cease and 
give place entirely to rain. Melting would then 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. Next 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 neces- 
sary result from an increase of eccentricity. Now, 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 Norway, 
covered with snow and ice. Here a new and powerful agent 
would come into operation which would greatly hasten on a 
glacial condition of things. This large 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 sup- 
pose 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 present condition of 
Greenland. Were it not for the ice, the summers of North 
Greenland, owing to the continuance of the sun above the 
horizon, would be as warm as those of England : but, instead 
of this, the Greenland summers are colder than our winters, 
and snow during that season falls more or less nine days out 
of ten. But were the ice-covering removed, a snow-shower 
during summer would be as great a rarity as it would be with 
us. On the other hand, cover India with an ice-sheet, and the 
summers of that place would be colder than those of England. 
