1 66 The American Geologist. Septomber, i89» 
movement of the ice-body. In 1880 W J McGee expressed 
the view that the polar regions were never more extensively 
glaciated than at the present time. Similar views were ex- 
pressed by H. Carvill Lewis in 1886, who designated two cen- 
ters of ice accumulation and radiation, on the east and west 
sides of Hudson Bay, and in 1889 by Robert Bell, the Nestor 
of Canadian glacialists. 
Dr. G. M. Dawson in 1888 recognized a separate confluent 
ice mass in British Columbia between the Coast and Rocky 
mountain ranges, and in 1890 he gave names to two ice bodies, 
Cordilleran for the one in British Columbia, and Laurentian 
for the eastern one. which he regarded as surrounding Hudson 
bay. In 1895 J. B. Tyrell restricted the name Laurentian 
(Laurentide) to the mass east of Hudson bay, and gave the 
name Keewatin to the body west of Hudson bav. These 
three centers ("glacial radiants" of Claypole) were adopted by 
professor Chamberlin in his chapter on North American 
glaciology in the latest edition of Geikie's "The Great Ice 
Age." Dr. Dawson thinks the Keewatin and the Laurentian 
(Labradorian) centers should be regarded as constituting the 
"Laurentide group," as distinguished from the far-separated 
Cordilleran mass. 
Migration of Maxima. — The first definite suggestion of 
lack of contemporaneity in the growth and culmination of the 
glacial centers was made by Robert Chalmers in i8go. From 
study of till sheets, boulder trains, etc., in the area of conten- 
tion between adjacent ice centers Dr. Dawson, in 1895, 
thought there had been a migration of glaciation from the 
Cordilleran to the Laurentian plateaus; and in 1896 Mr. Tyrell 
made a further refinement by claiming that the Keewatin gla- 
cier center had its maximum later than the Cordilleran and 
earlier than the Labradorian; and that a fourth center over 
Greenland is in existence to-day. This theory of migration 
of maximum accumulation receives encouragement from the 
results of recent studies of the Alaskan and the Greenland 
ice sheets. While the Alaskan glaciers are believe-d to have 
been waning in later time, the Greenland ice cap has probably 
increased, at least on the east coast, during several centuries, 
or since the time of the Norse colonies. 
Thickness. — In 1883 J. C. Smock published an article on 
