264 W. J. McGee—Thickness of Ice-sheet at any Latitude. 
ArT. XXXVIII—On the thickness of the Ice-sheet at any 
Latitude ; by W. J. McGrEr.* 
1, ESTIMATES OF THICKNESS. 
First preliminary estimate.—It was shown in Part I of this 
tion, and hence of course the accumulation of ice, is propor- 
tional to the vapor-tension. If then the thickness at any lati- 
uted. . 
J Professor Dana has shown + that the thickness of the Quater- 
ternary ice-sheet over the Canadian highlands (about N. lat. 
48° to 50°) must have been at least 12,000 feet. As this accu- 
mulation took place under conditions less favorable than those 
considered in the present discussion, it may be assumed that 
a thickness of three miles might obtain at lat. 40°. The thick- 
ness at each latitude from 40° to the pole would accordingly be 
as represented in table XVII. The data forming the basis of 
Wiel cohana are derived from sources previously enumer- 
a 
Taste XVII. 
Greatest thickness of Ice-field from lat. 40° to the Pole, 
Latitnde. emperat Vapor-tension. Thickness of ice. 
40° 56°5° 0°457 in. 3°000 miles 
50 ALT 26 1-233 
60 30°2 “168 1103 
70 iGu. “090 1 
80 6°8 059 387 
90 2°3 048 315 
* This article is from Mr. McGee’s paper on ‘Maximum Synchronous beg 
tion,” making 65 pages of the Proceedings of the American Association 0} 
the Advancement of Science, vol. xxix, 1880. 
+ This Journal, March, 1873. 
