Glacier Work. — Scott. 247 
4. A period of greater moisture in the atmosphere. 
5. Variations in the amount of heat radiated by the =^un. 
6. A variation in the heat absorbing power of the sun's 
atmosphere. 
7. \'ariations in the temperature of space. 
8. A coincidence of an aphehon winter with a period of 
maximum eccentricity of the earth's orbit. 
9. A combination of Xos. 8 and 2. 
10. Ball. — "The Cause of an Ice Age." 
Dr. Croll's hypothesis appears to have done more to. stim- 
ulate inquiry upon this question than any other, although it 
must be regarded at present as incompetent to satisfy all con- 
ditions required of it. For example, his theory demands the 
alternate glaciation of the Arctic and Antarctic regions, but 
geologists find no evidence of such, alternat'on, while facts, 
however, go to show contemporaneous glaciation of these 
regions ; again, ice scratches and grooves seem to be equally 
fresh in both hemispheres, so that it does not seem that there 
can be a difference of 20,000 years in their ages as required 
by the theory ; and finally, the work done on the earth's sur- 
face since the ice passed away seems too little for the 80,000 
years which Dr. Croll supposes to have elapsed ^ince that time. 
The gorges of Niagara and St. Anthony support the view, 
it is claimed, that they are too small for the w'ork of their 
streams during such a period. Geologists are more disposed 
from the array of facts thus far collected, to place the time 
since the cold era at 10,000 to 15,000 years, than to admit 
Croll's hypothesis. 
It appears that the contest over the evidence of Quaternary 
glaciation was first developed concerning cold temperate 
latitudes, then for warm temperate regions, and has finally 
come to be confined largely to tropical countries. 
In a paper on "The supposed glaciation of Brazil," by 
Branner, * this author refers to the controversy over the 
question, alluding to the fact that Agassiz and Hartt on first 
inspection of the country, believed it to have been glaciated. 
Prof. Shaler states it as his opinion, however, that Agassiz 
^ave vip the idea before his death. Branner says that in his 
eisrht years of travel and geological observation over the 
*Jour. of GpoI. 1893. 
