257 Geology and Botany of Xortltern Pacific Railroad. 



a roche moutonnee. From the Three Sisters the glaciers descend- 

 ed into the valley of the Willamette on the west and that of the 

 Des Chutes on the east; and I traced with the barometer the gla- 

 cial markings, from the snow-line to a point 2500 feet lower, 

 where they pass under the alluvium of McKenzk-'s Fork.* 



THE FORESTS OF THK CASCADE MOUNTAINS. 



All the summits and western slopes of the Cascade Mountains 

 are covered with a dense forest, mainly of evergreens, of which 

 many of the trees are of gigantic dimensions. On the eastern 

 slopes, the prairies in places run up the mountain sides, but the 

 timber follows all the valleys down to the plain. East of the 

 mountains are scattered trees of the yellow pine (Pinus ponde- 

 rosa) and the western cedar (Juniperus occidental**), and in some 

 localities, as has been mentioned, groves and forests of the former. 

 The evergreens which cover the mountains consist of four spe- 

 cies of pine, viz., Pinus Lambertiana, P. monticola, P. albi- 



* It has been claimed by Lecoq (Les Glaciers el les Climats), and following 

 him, by Prof. Whitney and others (Later Climatic Changes), that the great devel- 

 opment of glaciers during the Ice Period, such as those of the Canadian 

 highlands, the Rocky Mountains and the Cascades, of which we have such 

 abundant evidence, was not the effect of a cold period, but a warm one, 

 which increased the precipitation and consequently the snow-fall, at all 

 places where the temperature was low enough to cause it to take the form 

 of snow. If this was all, however, the most extensive glaciers should be 

 in the Alpine districts of the tropics or of the temperate zones, wherever the 

 precipitation is most abundant and the temperature low enough to produce 

 perpetual snow. But we have, on the summits of the Cascades, a demon- 

 stration of the fallacy of this view ; since here some of the mountains rise 

 14,000 feet and the line of perpetual snow is not over 7,000 feet, while the 

 annual precipitation is greater than in almost any other portion of our 

 country. In fact the snow accumulates in such quantity that, even in mid- 

 summer, it reaches so low that it is met and opposed by a vigorous forest 

 growth, the product of a mild climate. It is evident that no elevation 

 of temperature, though it should increase the evaporation on the Pacific and 

 the rainfall on the coast, would cause the renewal of the ancient glaciers ; 

 but with a depression of temperature which should continue the present 

 winter conditions through the year, the precipitation remaining the rcame, 

 the accumulation would soon cover the mountain summits with snow and 

 ice and bring the glaciers down to their old limit. 



