WoeiJcof—CrolVs Hypotheses of Geological Climates. 177 



I take another example from the southern hemisphere. Its 

 general geographical conditions are favorable to glaciation, but 

 by far not 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 dis- 

 agree also with Mr. A. R. Wallace* as to the condition of 

 this continent being a proof of the influence of winter in aphe- 

 lion on glaciation. Besides what is stated above as to the con- 

 ditions 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 (above 14,000 feet). Only in the western part 

 of the continent, and south of 35° S. is glaciation prevailing. 

 But where, in the northern hemisphere, have we so enormous 

 an extent of sea westward, with such regular and brisk west 

 winds, bringing an immense quantity of vapor, which is con- 

 densed into snow ? The amount of precipitation on the west 

 coast and the western slope of the mountains of South America, 

 south of 40° S., is scarcely equaled anywhere in the tropics. 

 Here again, geographical causes explain the result. The same 

 may be said of the west coast of the southern island of New 

 Zealand. Here also high mountains rise, and to the west is an 

 immense stretch of ocean, uninterrupted to the east coast of 

 South America. The snowfall is enormous and glaciers reach 

 to 700 feet above sea-level under 43° S. and yet the mean tem- 

 perature at sea-level is higher than in other meridians of the 

 southern hemisphere and the greater part of the northern also. 



In the two examples given above, evaporation takes place 

 from seas of relatively high surface temperature, about 50° F. 

 or more, and in such cases permanent snow can begin, only at 

 a height of some thousand feet, because air rising to such a 

 height is cooled by expansion and its vapor precipitated in the 

 form of snow. Mr. A. B. Wallacef has very well shown the 

 importance of high land for glaciatiou, though, to my mind, he 

 has gone too far in not admitting the possibility of glaciation on 

 low lands. 



I must conclude. An English geologist of note:}: has 

 called Dr. Croll's hypotheses brilliant and fascinating. So 

 they certainly are. The originality of the conception, the fer- 

 tility of resource of the author, his indomitable will, are sym- 

 pathetic in the highest degree. It is with a melancholy feeling 

 that I confess that interesting and important as are some parts 

 of the system of Dr. Croll, the main points of it are opposed to 

 the most certain teachings of meteorology and can not be 



* Island Life, page 142 f£. f Island Life. % Mr. Searles "Wood, Jr. 



Am. Jour. Sci.— Third Series, Vol. XXXI, No. 182.— Mar., 1886. 

 12 



