240 Dr. A. Woeikof on Geological Climates. 



such regular brisk west winds, bringing an immense quantity 

 of vapour, which is condensed as snow ? The amount of pre- 

 cipitation on the west coast and the western slope of the moun- 

 tains of South America, south of 40° S., is scarcely equalled 

 anywhere in the tropics, and, besides, the greatest part falls 

 in the cold season. The same may be said of the west coast 

 of the southern island of New Zealand, where also high 

 mountains rise, and to the west is an immense stretch of 

 ocean, uninterrupted to the E. coast of South America. The 

 snowfall is enormous, and glaciers reach down to 700 ft. above 

 sea-level ; and yet the mean temperature 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 exist bat at a 

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

 height is cooled by expansion, and its vapour precipitated in 

 the form of snow. Mr. A. R. Wallace * has very well 

 shown the importance of high land for glaciation; 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 f has 

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

 they certainly are. The originality of the conception, the 

 fertility of resource of the author, his indomitable will, are 

 sympathetic in the highest degree. With a melancholy 

 feeling I must state 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 

 cannot be accepted. Besides the purely geological and cosmo- 

 logical part of his work, which I do not consider here, and the 

 tables of excentricity, what can be accepted ? The wind theory 

 of the upper oceanic currents, the notion of the great clima- 

 tological effects of these currents (though by no means in the 

 exaggerated extent given to them by Dr. Croll), and some of 

 his considerations on the conservative effects of snow and ice. 

 The main points on which rests, so to speak, the whole fabric in 

 its explanation of glaciation and geological climates generally 

 — the influence of ivinter in aphelion and perihelion during high 

 excentricity and the calculation of temperatures in proportion to 

 the sun-heat received — are, unfortunately, not acceptable. 



Geologists will have to look for other causes to explain the 

 more or less frequent glacial and interglacial periods, which 

 their studies lead them to admit. 



* < Island Life.' t Mr. Searles V. Wood, jun. 



