108 JOUENAL OF SCIENCE. 



Lewis, in a lecture published in the Journal of the Franklin Institute 

 for April, 1883, says, ' It probably also filled the bed of the Atlantic 

 with ice far south of Greenland, the edge of the glacier reaching from 

 Newfoundland to southern Ireland in a concave line ;' and Professor 

 Geikie says the German Ocean was entirely filled with ice. Similar 

 evidence has been found as to the antarctic glacier. We have therefore 

 two magnificent circular polar ice-caps, each of them nearly 7,000 miles 

 in diameter, and the two covering about 61,000,000 square miles of the 

 earth's surface, leaving a zone of non-glaciated surface at the equator of 

 about 130,000,000 square miles; so that, at the culmination of the 

 glacial epoch, nearly one-third of the earth's surface was covered with 

 ice. 



" If, now, we could ascertain the thickness of these great glaciers, 

 we could easily estimate the amount of the earth's mass taken up in 

 the form of aqueous vapour, transferred to the polar areas, and there 

 deposited in the form of snow and ice. While admitting the incom- 

 pleteness of the record, the weight of the evidence at present is to the 

 effect that the antarctic glacier was much larger than the arctic. Upon 

 general reasoning, this ought to have been true ; for three-fourths of 

 the land surface of the earth are in the northern hemisphere, and the 

 amount of water suface in the southern and northern hemispheres res- 

 pectively is in the ratio of 85 to 60. In the southern hemisphere, 

 therefore, there ought to have been a greater amount of evaporation ; 

 and, in the absence of any known air-currents to carry this evaporation 

 to the north of the equator, there would necessarily be a greater amount 

 of precipitation in the southern hemisphere, and consequently a greater 

 accumulation of ice. That such was the fact in glacial times, seems to 

 be indicated by what is conceded to be an imperfect record. Professor 

 Dana, in his ' Manual of Geology,' estimates the thickness of the 

 northern glacier in America to have been 11,500 feet on the watershed 

 of Canada. Professor Le Conte, in his ' Elements of Geology,' says, 

 ' The archsean region of Canada seems to have been . . . covered 

 with a general ice mantle 3,000 to 6,000 feet thick ;' and Professor 

 James Geikie says the Scandinavian ice-sheet ' could hardly have been 

 less than 6,000 or 7,000 feet thick.' As Norway extends nearly to the 

 7'2nd parallel of north latitude, it is not probable that the northern 

 glacier exceeded two miles in thickness at its greatest height. Professor 

 Le Conte says, ' Greenland is apparently entirely covered with an 

 immense sheet of ice, several thousand feet thick, which moves slowly 

 seaward, and enters the ocean through immense fiords. Judging from 

 the immense barrier of icebergs found by Capt. Wilkes on its coast, the 

 antarctic continent is probably even more thickly covered with ice than 

 Greenland.' Sir James Clark Ross reports having sailed for several 

 hundred miles along a perpendicular wall of ice 180 to 200 feet high in 

 the antarctic continent, and found only one place where the top of the 

 ice could be seen from the mast-head of his ship ; and Capts. Cook and 

 Wilkes both confirm the report of a large ice-sheet in that part of the 

 world. Professor Croll, in ' Climate and Time,' estimates from all the 

 data at hand, that the thickness of the southern ice-cap at its greatest 

 height is no less than twelve miles. It is not probable that the 

 antarctic glacier was much, if any, higher than this in glacial times; for 

 it will be readily understood, that, after the glaciation had proceeded so 



