J. Croll— Cause of Mild Polar Climates. 139 © 
Tertiary times, that consequently the climatic condition of that 
period was not much affected by eccentricity. 
together with many others. The question which presents itself 
° one’s mind, he remarks, is, how is it possible that the tropi- 
‘al forms, such as the palms, aroids, cactus, ete., could have 
8rown alongside of the apparently temperate forms, such as the 
an elm, beech, and others? Mr. Gardi ner’s explanation is as 
i rn 
