246 The American Geologist. October, 1902. 
similar and contemporaneous ice mass is evidenced.extending 
over Canada and the north-eastern United States, exhibiting 
tlie same characteristic work as that of the old world. The 
thickness of the ice is shown by the fact that the Catskill moun- 
tains are glaciated near their summits at a hight of 3,000 feet. 
The White mountains are said to be ice worn at a hight of 
5,500 feet ; '•' ice worn surfaces have been found in New 
South Wales at elevations between 4,000 and 6,000 feet; and 
Dawson speaks of glaciated surfaces in British Columbia at a 
hight of 7,000 feet above the sea.f 
Origin of the Ice-Agc. 
As to the origin of an Ice-age, which is a subject of great 
curiosity, if not, indeed, of supreme importance, the theories 
of eminent men are so at variance with each other, that it 
seems practically impossible to arrive at a satisfactory 
conclusion. 
Geologists, astronomers, ph}-sicists, have vied with each 
other in the establishment of an infallible theory, but in view 
of the fact that the question is open for further efforts, the 
writer would in passing merely refer to a small part of the 
literature upon this point, t 
The leading causes of an ice age that have been propounded 
are well set forth in a series of papers on, "The Evolution of 
Climates," by ]\Iardsen AIanson.§ He enuuicrates them as 
follows : 
1. A decrease in the original heat of the globe. 
2. Changes in the elevation of the land, and consequent 
variations in the distribution of land and water. 
3. Changes in the obliquity of the axis of the earth. 
♦Archibald Geikle, Text-book. pp. 1050. 
tGeol. Mas. i8S9, p. 351. 
J Sir Robert Ball, Nature, Vol. 25, 1S81, pp. 79-103. 
Darwin, Trans. Nature, Vol. 25, 1881. 
Lord Kelvin, Trans. Geol. Soc, Glasgow, Vol. 5, p. 238. 
Tait. Recent Advances in Phvsical Sci. 1876. 
Dr. M. Neumayr, Nature, Vol. 42, 1890, p. 148. 
L^'ell. Principles of Geolo&j'. 
Sir John Herschell. Trans. Geol. Soc. .Glasgow, Vol. 3, p. 293. 
Dr. James Croll, Phil. Mag., Vol. 28, p. 121, also. 
Climate and Time, and Discussions on Climate and 
Cosmology. 
A. Falsan and E. Chantre, Ancient Glaciers. 
J. Partsch, Die Gletscher der Vorzeit in den Karpathen. 1SS2. 
T. C. Chamberlin. Jour, of Geology. Vol. 7. 1899, pp. 545, 6G7, 751, Amer. 
Jour, of Sci.; Ann. Reports U. S. Geol. Survey; Bull. Geol. Soc. of Amer- 
ica; Jour, of Geol.; and Amer. Geologist, for the last ten or fifteen years^ 
§Am. Geol., Vol. xsiv, pp. 93, 157, 205. 
