The Evobition of Climates. — Mansoii. 107, 
is in existence now in both torrid and temperate latitudes, and 
is recording the evidence of its action in the same manner as 
heretofore, but it is not accompanied by corroborative evi- 
dence. It is not therefore permissible to advance the theory 
of a present ice age over tropical and temperate latitudes. It 
present glacial action in these latitudes descended to sea level 
and were it accompanied by marine life of arctic types, and 
were temperate and tropical forms absent, the existence of a 
glacial period would be established, but glacial action alone is 
not sufficient evidence upon which to base the occurrence of 
a glacial period. We should be cautious, therefore, in build- 
ing up a glacial period upon insufficient data in any geological 
age. 
The Relation of Present Glaciers to the Problem. 
Wherever within tropical or temperate areas glaciers yet 
rest, they are at once recognized as the feeble remnants of once 
vaster extensions.* Therefore at the outset is established the 
fact that glacial conditions have been much more extensive 
than at present and that they are yet retiring. Consequently 
there confronts us at once the problem of accounting for this 
past extension and present retreat. The student may start 
at the base of the great Malaspina glacier of Alaska, lat. 60° 
N., and follow the evidences of past glacial action into the 
tropical regions, through the just uncovered pleateaux, fiords, 
and mountains of British Columbia, lat 50° ; through the yet 
earlier uncovered and fainter traces in the Sierra and Coast 
range of California, lat 42° to 35°; through Mexico, lat 30° to 
15°; even with Belt and Crawford, through the barely traceable 
markings of Nicaraguan glaciers, in lat. 12° to 8° N. 
Starting at the confines of the south frigid zone the same 
gradations of distinctness in glacial markings can be traced 
northwards, until they fade in the highly modified and indis- 
tinct evidences within the tropics. 
Again, the student may ascend 16,000 to 20,000 feet above 
*Prof. I. C. Russell, Am. Geo!. , Vol. IX, No. 5. May. 1892. In 
addition to the extended list of authorities cited by Prof. Russell see 
also the article by Prof. Dufour, Bulletin Soc. Vaud. Sc. Nat., Vol. 
XVII, 1891, pp. 422-425; Report Brit. Assn., 1881, p. 742; "Life of 
Agassiz," Vol. II, pp. 717-729, also pp. 743-747- The Great Ice Age, 
p. 711 et seq. pp. 721-2 (3rd Edition Re-wriitten), Dr. James Geikie, 
New York, 1895. 
