252 ANNUAL REPORT SMITHSONIAN INSTITUTION, 195 2 



In the sea cliffs of Herschel Island, in the Beaufort Sea west of the 

 mouth of the Mackenzie River, extensive beds of soil and clay con- 

 taining twigs and at least one log are exposed (O'Neill, 1924, p. 12). 

 Again, near the mouth of the Ikpikpuk River, on the arctic coast of 

 Alaska east of Point Barrow, spruce logs occur in the sediments of 

 the coastal plain (Smith and Mertie, 1930, p. 254). Large logs are 

 found in the superficial deposits of the Kuzitrin lowland north of 

 Nome, Alaska (Collier et al., 1908, pp. 89, 91). Little is known 

 about these deposits but, as their localities lie beyond the present 

 poleward limit of trees, the material may be interglacial. We cannot 

 state the inference more strongly than this, because the possibility 

 that the twigs and logs were simply driftwood, perhaps from distant 

 points of origin, has not been eliminated. 



There is clear evidence of at least two glacial ages in the frozen 

 ground in the Yukon River basin in central Alaska, although the 

 region was never glaciated because it is low, dry, and subject to warm 

 summers. This country is underlain by thick beds of silt, deposited 

 mainly by the Yukon and other rivers. As it lies within the arctic belt 

 of perennially frozen ground, most of the silt is frozen to depths 

 reaching hundreds of feet. Mining operations have exposed extensive 

 sections of the silt, overlain by thick mudflow deposits consisting of 

 thawed silt, now refrozen. Such sections furnish evidence of an epi- 

 sode of deep thaw that intervened between two episodes of deep 

 freezing (Taber, 1943). As freezing and thawing well below the 

 surface take place slowly, a long interval of warmth is indicated. 

 These events, however, have not yet been firmly dated. 



In northern British Columbia and also on the east coast of Green- 

 land the forms of major valleys seem to indicate a period of deep 

 stream trenching that occurred between two periods of glaciation. 



These are the scattered pieces of evidence of repeated glaciation de- 

 rived from the arctic region. Many more will be discovered, but they 

 are not likely to approach either in quantity or quality the records 

 from the southern margin of the glaciated region. 



A great variety of evidence has established the belief that since the 

 latest of the glacial ages reached its peak several tens of thousands 

 of years ago and began to wane, the climate has not become continu- 

 ously milder. The record shows that in northern Europe and tem- 

 perate North America, at least, climates attained a maximum of 

 warmth and dryness roughly 5,000 years ago ; since when, conditions 

 have become appreciably cooler and wetter. It has been shown that 

 some of the glaciers in western United States had dwindled away or 

 disappeared entirely during the period of warmth and were later re- 

 born. Arctic America is not likely to have undergone so drastic a 

 change because of its cooler climate, but nevertheless it is likely that 



