noLMEsJ VALLEY OF GARDINER RIVER. 27 



small spiral shell, tliat is thought by Dr. White to be Jurassic. As- 

 sociated with the limestones is a seam of hornblendic trachyte haviug 

 the same dip and strike as the sedimentary beds. Above this and 

 forming the crest of the ridge is a heavy stratum of quartzite, beneath 

 which, on the northern slope, I found the heavy conglomerate so char- 

 acteristic of No. 1 Cretaceous. In this part of the range the strata rise 

 at a slight angle toward the crest of the range, 3 to 4 miles to the 

 west; in places — noticeably about the head of the main Gardiner, 

 southwest of the base of Electric Peak — there are occasionally more 

 abrupt dips, as much as 10° and 12° to the northeast. This spur is the 

 first prominent one south of Electric Peak and descends in an irregular 

 slope, composed of the Lower Cretaceous and possibly Jurassic rock, 

 to the bed of the main branch of Gardiner River, l^orth of this stream 

 the Cretaceous strata appear in full force in the broad steep face of Elec- 

 tric Peak. At the base are a number of beds of sandstone probably 

 belonging to the Dakota Group, upon which rest a thickness of 3,000 

 feet of dark slates and shales. It is worthy of notice that the dip and 

 strike of these beds correspond pretty closely to the dip and strike of 

 strata of corresponding age in Mount Evarts and the valley of the Gar- 

 diner about the Hot Springs. 



Just what agencies conspired to break the continuity of the strata, I 

 cannot determine. Much of the erosion has been accomplished by the 

 present drainage, but the abrupt eastern wall of the Gallatin Eange can- 

 not have been produced in that way. The present valley of Cache 

 Creek is probably due chiefly to erosion by its own waters, but the 

 break in the strata, which at one time were continuous from the Galla- 

 tin Range to Mount Evarts, existed before the formation of the present 

 valley, and even before the conglomerate deposits of Sepulchre Mount- 

 ain existed. (See section, Plate X.) 



Crossing the river at the point of its exit from the mountains, I as- 

 cended a low rounded ridge that reached far down into the broad val- 

 ley of the Upper Gardiner. On the left there is a rather steep, wooded 

 descent to the West Gardiner. Beyond this rise the smooth slopes of 

 Sepulchre Mountain. On the right is the sage and grass-covered val- 

 ley of the Main Gardiner. The exposures of strata are very limited, on 

 account of the prevalence of drift materials. The summit of the ridge 

 is composed of coarse basaltic conglomerate, which is like the conglom- 

 erates of Sepulchre Mountain. 



UPPER GARDINER. 



I have already pretty fully described the lower valley of Gardiner 

 Eiter. My acquaintance with the upper valleys, of which there are 

 three, is almost entirely confined to the western, and but for the apparent 

 simplicity of the geologic construction I would not attempt a description. 

 Still, there are some very interesting points that may properly be men- 

 tioned here. Topographically, the chief features of the upper valley 

 are the great plateau and the isolated mountain (Bunsen's Peak) that 

 lies upon the plateau border, overlooking the Hot Springs, and which 

 forms such a marked feature in the landscape of the neighborhood. 



I have already described the manner in which the Cretaceous strata 

 exposed in the lower valley pass beneath the sheet of rhyolite that crowns 

 the opposing walls and circles the head of the valley, and mentioned 

 the probability that this rhyolite sheet has at one time been continuous 

 across the valley. It seems to me plain that at the time of the flow of 

 these sheets of rhyolite the northern border of the great basin into 



