258 Annals of the Carnegie Museum. 



certain evidence that deposition was continuous across the range here 

 in later Tertiary times. The rocks mistaken for Oligocene or Miocene 

 more resemble those of Laramie or Fort Union age in other places. 

 Soon, in descending Beaver Creek, sedimentary rocks disappear, and 

 only eruptive rocks are seen. The creek after flowirjg through two or 

 more basins for several miles, cuts a narrow canon through the 

 basalt. The railroad passes through this canon, while the wagon road 

 goes over hills and benches. The mountains on the east and west are 

 not high, and they decrease in height to the southward. Along the 

 stream is a thick growth of trees and shrubbery, while on the hills and 

 mountain slopes are sage-brush and coniferous trees. Besides these the 

 trees common along nearly all the streams of Montana, birch {Betula), 

 kinnikinick {Cornus), and black-fruited hawthorn {Cratcegus) were 

 seen. 



After descending the stream about sixteen miles from the Conti- 

 nental Divide, the mountains ceased, and to the southward, as far as 

 could be seen, was an arid plain, on which were comparatively few 

 landmarks. In an embayment of this plain beside a mountain stream, 

 nestled between the spurs of the foot-hills, is the little town of Spencer. 

 From this point I followed the road which goes eastward south of the 

 mountains near the northern border of the plain. Possibly some of 

 the rock in the higher portion of the range is of sedimentary origin, 

 but nearly all that of both plain and mountains is eruptive. Water- 

 courses, making ravines and canons, start away to the northward in 

 the main divide and score the sides of the mountains to the plains, on 

 which they sometimes continue for a short distance. Their course is 

 marked by a fringe of trees and shrubs, but most of them soon die out 

 on the arid waste of sage and sand. The stream (Beaver Creek), 

 which I had followed from Montana, cuts its way out into the rock of 

 the plain, and its course can be traced in some places by the trees, the 

 tops of which project above the narrow gorge. Most of the streams 

 were dry where the road crosses them, but in some there was water 

 higher up ; and there are occasional irrigated ranches between the 

 foot-hills. When approaching the valleys, which open from the foot- 

 hills, it looked as if the streams had their sources in the desert and 

 cut their way into the mountains. In fact the topography of the 

 country was so different from anything which I had previously seen, 

 that I often could not tell which way the land sloped, or make 

 out whether we were going on level ground or slightly up or down 



5 



