Dr. Croll's Hypotheses on Geological Climates. 239 



to snowfall and glaciation than those around Great Britain,, 

 because they are colder, and than those of the North- American 

 archipelago, the Kara Sea, and the Arctic Ocean about Siberia, 

 because they are less ice-bound in the cold season. 



4. The intense glaciation of the highest southern latitudes 

 gives an enormous quantity of icebergs floating northwards, 

 i. e. to the seas of lower latitudes. As the surface of the 

 southern seas to about 62° S. is below 32° F., even in mid- 

 summer, the icebergs cannot melt till they reach that latitude, 

 and their immense size enables them to reach sometimes 

 even the 35th parallel S. They certainly cool the waters, 

 and thus produce conditions favourable to glaciation even 

 in lower middle latitudes. This, besides, is a further direct 

 cause of lower temperatures, and an indirect cause of stronger 

 and more extensive trade-winds, which reach to beyond the 

 equator and bring much warm water to the northern hemi- 

 sphere. The geographical position is also favourable to this, 

 especially the situation of Cape S. Roque and its vicinity. 



It is easy to see from all this, that there is no necessity to 

 seek far for the reason of the difference of the northern and 

 southern hemispheres as to glaciation, without calling in aid 

 the winter in perihelion of the former and the winter in aphe- 

 lion of the latter ; much simpler causes explain the result. 

 The operation of these causes is exceedingly well illustrated 

 in the glaciation of a part of the higher latitudes of the 

 northern latitudes, while to the east and west there is none, 

 with lower mean annual temperatures. 



I take another example from the southern hemisphere. Its 

 general geographical conditions are favourable to glaciation, 

 but by no means everywhere equally. Thus the higher 

 latitudes of the eastern part of South America have as little 

 snow, even in winter, as the warmest parts of the European 

 continent under the same latitudes ; while a degree or two to 

 the south, South Georgia is deeply glaciated. As to South 

 America, I must disagree also with Mr. A, R. Wallace * as 

 to the condition of this continent being a proof of the influence 

 of winter in aphelion on glaciation. Besides what is stated 

 above as to the conditions of the eastern part of the continent, 

 I may mention the absence of snow and glaciers from the 

 highlands of the Atacama Desert (above 10,000 feet high), 

 and those between the coast and Lake Titicaca (about 14,000 

 feet). Only in the west of the continent, and south of 35° S., 

 does glaciation prevail. But where, in the northern hemi- 

 sphere, have we so enormous an extent of sea westwards, with 



* ' Island Life/ p. 142 and foil. 



