DEARTH OF GLACIAL RECORDS IX ALASKA. Ill 



escarpments, which, as shown by the nearly complete removal of such material 

 in the region occupied by the Cordilleran glacier, could not have retained 

 their characteristic shapes had they been subjected to glacial action. 



Not only is there proof of the absence of a general ice sheet over the 

 greater part of the extensive region indicated above, but the mountains 

 seen from the Yukon, several of which are fully 4,000 feet in elevation, are 

 without evidence of local glaciation. There are no cirques about their 

 summits or wide canons with lateral or terminal moraines on their sides. 

 AH of the mountains here referred to are near, and some of them are north 

 of, the Arctic circle, yet they are now completely bare of snow throughout 

 the summer. This indicates that existing climatic conditions are analogous 

 to those prevailing in the same region during the glacial epoch. 



Absence of Glacial Records along the Porcupine.— I saw no evidence of 

 glaciation along Porcupine river, and my observations in this matter agree 

 with McConnell's. At the highest point reached by me on the Porcupine 

 the hill-tops, having an elevation of about 400 feet above the river, were 

 covered with well-worn gravel. These are probably stream gravels, and 

 correspond to the high terraces observed in the upper portion of the Yukon 

 and along the Lewes. 



The Snow Line. — It is stated in many works on geography that the lower 

 limit of perennial snow occurs at an elevation of about 18,000 feet in the 

 tropics, decreases in elevation towards the north and south, and reaches sea 

 level in the antarctic and arctic regions. Alaska and the North West 

 Territory offer marked exceptions to this supposed rule. The snow line in 

 southern Alaska is at an elevation of about 3,000 feet, and increases in 

 height towards the north. John Muir* says — 



" There is no line of perpetual snow on any portion of the arctic region known to 

 explorers. The snow disappears every summer not only from the low sandy shores 

 and boggy tundras but also from the tops of the mountains and all the upper slopes 

 and valleys with the exception of small patches of drifts and avalanche-heaps hardly 

 noticeable in general views. But though nowhere excessively deep or permanent, 

 the snow-mantle is universal during winter, and the plants are solidly frozen and 

 buried for nearly three-fourths of the year." 



GLACIATION IN THE UPPER YUKON REGION. 



Previous Explorations.— -The glaciation of the region drained by the head- 

 waters of the Yukon has been described by Dawson and McConnell, as 

 already stated. 



The records of ice action in this region are smoothed, polished, and striated 

 rock surfaces, perched bowlders, and deposits of bowlder clay. Distinct and 

 well-defined moraines have not been observed, and the country generally is 



* Botanical Notes on Alaska, in Cruise of the Revenue-Steamer Corwin in Alaska and the N. W 

 Arctic Ocean in 1881. Treasury Department, Washington, 18813, p. 17. 



