GEOLOGICAL SURVEY OF THE TERRITORIES. 117 



a portion of the soutliern shore of the ancient lake, as the Brid^er Range 

 did part of the eastern shore, while Mount Ellis and Bridger Peak may 

 have been promontories projecting into it. The action of volcanic 

 forces within a very short distance, however, has complicated matters 

 to such an extent that any opinion must be conjectural, and future 

 careful study will be required to prove or disprove. The elevation of 

 the lake above sea-level is 6,408 feet, which is 1,533 feet higher than the 

 elevation of our camp at Fort Ellis. The synclinal valley, which I 

 referred to above, has no later rocks than the Cretaceous. Why there 

 should be no Tertiary beds here is perhaps a little difficult to understand. 

 That there have never been any is evident, or there would be some 

 remnant or trace of them left. Erosion could scarcely have removed 

 all without some trace being left. Moreover, this is not a valley caused 

 by erosion. Perhaps the elevation of this point, which may have been 

 greater in the past, precluded the possibility of the Tertiary beds reach- 

 ing this point. 



Bozeinan Creek, leaving Mystic Lake, flows at first a little west of 

 south, and turning flows more toward the west, until finally it flows in 

 a northwesterly direction. At first it cuts its way in a deep gorge 

 almost at right angles to the strata, over which it rushes in a series of 

 cascades half hidden by the overhanging vines and brush. Within a 

 quarter of a mile it falls about five hundred feet. Just below the lake 

 it is joined by a stream coming in from the left. It heads at the base 

 of the volcanic range, which lies to the east of Mystic Lake. Following 

 the course of this creek there is a bed of volcanic breccia which has 

 flowed from the head of the valley. It is composed of sharp angular 

 fragments of basalt, varying in size from three inches to a foot. The 

 prevailing colors are black and a brick red. The cementing material of 

 this breccia seems to contain fragments of sandstone like those seen in 

 the Eocene beds. The belt covered by this bed of breccia is not over a 

 quarter of a mile in width. 



The minerals I obtained while at Fort Ellis are as follows, viz: rhomb- 

 spar, dog-tooth spar, quartz, agate, red and yellow jasper, and coal. 



We left Fort Ellis on the 2Uth of July and started for the valley of 

 the Yellowstone. For ab6ut three miles our course was in an easterly 

 direction, when we turned toward the southeast and followed one of the 

 branches of Mill Creek, the stream that flows through Spring Caiion. 

 Our road led ns over Tertiary sandstones. Camp No. 2 was in a mouo- 

 clinal valley, near the head of Mill Creek. The hills on the east side 

 of the valley were Tertiary, while those on the west, dipping in the same 

 direction, were Cretaceous. The former were about 400 feet high and 

 composed of sandstones, the texture of which varied, some of the layers 

 being quite soft, while others were very hard, seeming to have been met- 

 amorphosed. Many of them contained impressions of deciduous leaves, 

 which Professor Lesquereux has determined to be Eocene. Among 

 them he found Platanus aceroides, Fagus antqmfi, SaUshuriapoJymorpha, 

 Juglans denticulata, and Gymnogramma Haydcnii. He says, "The most 

 interesting discovery is that of Salishuria polymorpha, described from 

 Evan's specimens of Vaucouvers Island, a long time ago." This would 

 indicate a correspondence in the Tertiary flora of the Pacific coast, and 

 that on the east side of the liocky Mountain divide as at present consti- 

 tuted, and thus points to the modern elevation of the range. Mr. Meek 

 finds also a correspondence in the Cretaceous shells of the two localities 

 referred to, and says also that they do not correspond to the forms found 

 farther east, which would lead ns to suppose that at the period of their 

 deposition the divide of the Kocky Mountain must have been more to the 



