((LACTATION DUE TO LOCAL CLIMATE. L53 



The absence of perennial snow on the mountains of the Yukon region has 

 already been referred to. A similar absence of snow has been reported by 

 McConnell along the lower McKenzie. The reader will recall also that the 

 glaciers on the north side of the Coast Range of Alaska are very much 

 smaller than, and do not descend nearly so far as, the glaciers on the south 

 side of the same range. Closely related to the distribution of the glaciers 

 are certain climatic phenomena. 



In the Yukon region the winters are long and extremely cold ; a temper- 

 ature of minus 80° Fahrenheit, I have been informed, not being uncommon. 

 The mean annual temperature of this region as shown by Dall * is between 

 ten and twenty degrees Fahrenheit. The snow-fall, however, is not great ; 

 perhaps two or three feet, on an average. The summers, though short, are 

 pleasant, and hot enough to melt the winter's snows. The large number of 

 hours of suushine in summer greatly assists in raising the mean temperature 

 at that season. 



Ou the southern coast the winters, though long, are not severe, a fall of 

 the thermometer to zero Fahrenheit, being seldom experienced at Juneau 

 or Sitka. The snow-fall is heavy on the mountains, and rain is abundant 

 on the immediate coast. The summers are cloudy and wet, with much fog; 

 the number of clear days being few. The mean annual temperature on the 

 coast as given by Dall* is in the neighborhood of forty degrees Fahrenheit. 

 The rainfall during the only year in which continuous observations were 

 made at Juneau was over 103 inches.f 



These observations show that the abundant precipitation on the southern 

 coast of Alaska, accompanied by a low mean annual temperature (due es- 

 pecially to a cool and cloudy summer), has resulted in the formation of vast 

 ice-fields from which magnificent glaciers descend to the sea. 



The excessively cold winters of the interior, followed by comparatively 

 clear and warm summers, are not accompanied by an accumulation of 

 perennial snow even on mountaius three to four thousand feet high and 

 situated under the Arctic circle. 



The southern shore of Alaska rises from the ocean to a great height, and 

 furnishes a cold surface against which the warm, moist southeru winds im- 

 pinge and are forced upwards. These favorable conditions for the formation 

 of glaciers are still farther augmented by the presence of warm currents in 

 the Pacific. A vast evaporating surface and a cold condensing surface are 

 here close together. 



The intimate dependence of the Alaskan glaciers on existing topographic 

 and climatic conditions suggests certain interesting hypotheses in reference 

 to the occurrence of continental glaciers in other regions and perhaps in 

 various geological epochs. 



* Pacific Coast Pilot, second series, U. S. Coast and Geodetic Survey, Washington, 1879, pi. 20. 

 t MSS. of observations made by Karl Koehler from Nov. 1, 1883, to Nov. 1, 1884. 



