[08 ABSTRACTS 



excavated by Snake River. From the mouth of^Snake River to Lewis- 

 ton, the stream is a narrow^, deep-sided canyon, about 2000 feet deep. 

 Where Snake River forms the boundary between Washington and 

 Idaho, its gorge is about 4000 feet deep and fifteen miles broad. 

 Within this vast canyon there are many lateral ridges, and a great vari- 

 ety of topographic forms due to erosion. This portion of Snake River 

 canyon compares favorably with even the most magnificent parts of the 

 Grand Canyon of the Colorado, except that it lacks the gorgeous col- 

 oring to which so much of the charm of its southern rival is due. The 

 thickness of horizontally bedded basalt exposed in the walls of Snake 

 River canyon and in the adjacent Blue Mountains, is in the neighbor- 

 hood of 5000 feet, but the maximum thickness is not exposed. In the 

 walls of the canyon at three localities, the summits of steep, angular 

 mountain ranges are revealed. One of these buried peaks rises about 

 2500 feet above the river and is covered by fully 1500 feet of horizon- 

 tally bedded basalt. The sheets of clay, sand, and gravel interleaved 

 with the basalt, especially near its junction with the bordering moun- 

 tains, furnish conditions favorable for obtaining artesian water. A 

 number of flowing wells derive their water supply from this source. 

 The Blue Mountains, at least at their northern extremity, consist of a 

 low, flat-topped dome of Columbia lava, which has been deeply dis- 

 sected by consequent streams. The surface of the basaltic plateau is 

 covered with residual soil which has an average depth of sixty to eighty 

 feet over thousands of square miles. The soil is exceedingly fine, dark 

 brown or black in color, and of wonderful fertility. This is the soil of 

 the celebrated wheat lands. The subsoil is fine, light yellowish in 

 color, without stratification, and in many localities traversed by 

 minute, irregular, but, in general, vertical tubes. In many ways the 

 subsoil closely resembles loess. Its origin from the disintegration and 

 decay of the underlying basalt is clearly manifest. 



Topographically the Columbia lava presents great diversity. In 

 the Blue Mountains there is an intricate series of sharp-crested ridges, 

 separated by a labyrinth of canyons, having in general a depth of 

 about 3000 feet. Between the Blue Mountains and Snake River there 

 are broad remnants of the nearly level plateau, separated by narrow, 

 steep-sided canyons, in general 2000 feet deep. North of Snake River 

 there is a vast area without deep canyons, but diversified by short hills 

 from fifty to eighty feet high, none of which, however, rises above a 

 certain general level. Along the eastern portion of this hilly plateau, 

 or rolling prairie as it was before cultivation began, there are a few 



