Douglass : A Geological Reconnaissance. 257 



smooth hills composed of coarse conglomerate. Hayden supposed 

 this to be of Carboniferous age ; but it would be interesting to know 

 whether it may not be the same as the Sphinx Conglomerate in the 

 Madison Range. If so, it is not earlier than Lower Eocene. In one 

 place north of the stream are beds near the river, which appear to be 

 of Oligocene age, though I did not have the opportunity of examining 

 them closely. South of the Centennial Valley I examined some gray 

 rocks, which are probably of Later Cretaceous age, and obtained some 

 fossil plants, among which are some very fine ferns. The species 

 have not been identified. 



As previously stated, one of the objects of the expedition was to 

 ascertain whether or not the Tertiary beds extend across the main 

 divide of the Rocky Mountains at Henry's Lake and near Monida, as 

 they do south of Silver Bow in Montana. South of Sage Creek the 

 Tertiary deposits, though I saw no outcrops beneath the basalt, appear 

 to " run under" the cap of lava which covers the tops of the high 

 hills. In fact I know of no place in Montana where it is positively cer- 

 tain that the large basaltic flows overlie the Tertiary. Farther south 

 than Sage Creek, on Red Rock Creek, several miles above Lima, as 

 previously stated, there are what appears at a distance to be Oligocene 

 deposits, along the stream. South of this I saw no outcrops. 



From Monida through Northern Idaho to Henry's 



Lake, Idaho. 



The Continental Divide and state line, between Montana and Idaho, 

 is only a short distance south of Monida, a little station on the Oregon 

 Short Line. Monida has an altitude of 6,803 feet. From Lima to 

 Monida, a distance of fifteen miles along the railroad, there is an 

 ascent of twenty-five hundred feet, but most of the way it is very 

 gradual, so that one does not realize that there is so much difference 

 in the altitudes of the two places. Southeast of Monida, the wagon 

 road ascends higher than the railroad. On the south side of the road 

 are rounded hills or mounds, which extend to a considerably higher 

 elevation. Immediately south of the divide streams begin, and flow 

 through broad upland flats or valleys. _ These are the sources of Beaver 

 Creek. On the eastern side of the main stream are rounded bluffs, in 

 which there are some exposures of a gray rock, which at a little 

 distance resembles the Tertiary rocks in Montana. But closer ex- 

 amination shows this to be a mistake, and there appears to be no 



