340 J. S. Newberry — Surface Geology of the 'country 



The bowlders are usually rounded, sometimes subangular, and 

 are composed of gray or red granite, quartzite, Paleozoic lime- 

 stone and a variety of eruptive rocks. The resemblance to the 

 drift from the Canadian highlands is so great that I was only 

 convinced of its local origin when I found all of its constituents 

 in place in the Belt and Rocky Mountains. The granites were 

 to my eye indistinguishable from those of the eastern Laurentian 

 series. As I subsequently learned, they are of Archaean age, 

 and nothing but careful microscopic examination will show 

 them to be distinguishable, if they are so. 



These facts lead me to suspect that the very careful and 

 experienced observers who have reported the finding of eastern 

 Laurentian bowlders on the flanks of the Rocky Mountains, 

 4000 feet above the sea may have been misled by this striking 

 resemblance. 



On the undulating surface of the table lands between the 

 tributaries of the Missouri, large bowlders are occasionally seen, 

 as in the States bordering the Great Lakes, and we passed one 

 of these somewhat angular in form which had served so long as 

 a rubbing-post for the buffaloes, recently abundant in this 

 region, that its sides are all polished, and a deep furrow is worn 

 around it by their feet. 



THE GORGE OF THE COLUMBIA. 



The gorge of the Columbia is one of the most impressive 

 and interesting topographical features in all the picturesque 

 West. It is cut with a nearly straight westerly course across 

 the whole breadth of the Cascade Mountains, fifty miles, and its 

 banks rise from 2,000 to 4,000 feet directly from the river side. 

 Most of the material of which the walls are composed is basalt. 

 This can be seen to form distinct layers, the products of differ- 

 ent overflows from the great volcanic vents north and south of 

 it. Cape Horn, a bold headland, shows a vertical face of trap 

 nearly 500 feet in height. 



No one who examines the gorge of the Columbia will fail to 

 be convinced that it has been cut by the river. The general 

 altitude of the mountains in which there are no other passes 

 lower than about 5,000 feet, as well as the altitude of the lake 

 deposits on the eastern side indicate that the work of cutting 

 this channel began at a height not less than 3,000 feet above 

 the sea. At this time the river must have had a fall of at least 

 this number of feet into the valley of the Willamette; and to 

 realize the conditions then existing, we must picture to our- 

 selves a series of cascades of greater magnitude and more 

 picturesque than any now known. This water-power was, 

 however, busily engaged in cutting down the barrier, and 

 in process of time it was so completely removed that a nav- 

 igable canal was opened from the Dalles to the ocean. The 



