260 GEOLOGICAL SUEVEY OF THE TEREITOEIES. 



trachyte. The valley is here wide and flat, mostly marshy, with some 

 large bayous. There are (considerable areas of fine graziiig-gromid aud 

 many large patches of willows. One island-like, rocky knob, with i^art 

 of the first terrace, which has been protected by it from erosion, stands 

 out in the middle of the valley, about a mile below the clilTs. The river 

 is here of moderate depth, with a bottom of small pebbles aud muddy 

 sand, but good fords are few and mostly difficult of access b}^ reason 

 of the marshes bordering the stream, so that the necessary crossing to 

 the east bank should be made near where our train crossed, unless 

 special reasons take one down the west side. As we approach the 

 lake, the stream gets deeper and more sluggish, being somewhat 

 checked by the back-water of the lake. Broad marshy flats stretch 

 back from the shore of the lake on both sides of the river. On all these 

 flats we find an abundance of " bitter cottonwood," which had formed, 

 higher up, only a very small i^art of the timber-growth, though its young 

 j)lants had, for the last fifteen or twenty miles, furnished rapidly-increas- 

 ing patches of yellow and pale-red along the slopes, thus replacing, in 

 some degree, the autumn-tints of the hickories, chestnuts, and maples 

 of more eastern regions, while a small mountain-ash was doing its best 

 to replace the deeper crimsons of the oaks and of some of the maples. 

 The development of these tints did not seem to be at all connected with 

 any special increase of cold ; and, indeed, we had been having frequent 

 freezes all the summer, without any apparent effect upon the vegeta- 

 tion, which seemed to be accustomed, as the grasshoppers are, to being 

 frozen up every nighL and thawed out every morning. 



The Teton Eange had been before us for many days as a prominent 

 feature of the landscape, but now its peaks stood up as the features of. 

 main interest, bounding the valley on the west with a series of roof-like 

 ridges and i)ointed peaks^ well besprinkled with patches of snow. 

 Farther north and east, we had been having i^leasant weather, while 

 this portion of the valley had several successive days of cloud and rain, 

 as reported from our guide, Beaver Dick, who met us again here, hav- 

 ing crossed from the valley of Henry's Fork. When these storms 

 reached the higher portions of the mountains, their deposit took the 

 form of snow, so that the drifts v.'ere now much larger than when we 

 struck the range on the other side, in July. 



On September 21, the minimum thermometer recorded 4:^^ ; and a 

 clear sky, with cool weather, gave us unusually fine views. The peaks 

 stood out sharply, while the gaps and canons were full of a deep-blue, 

 smoky light, which would touch the heart of the least artistic. 



On the northeastern slopes of the range, several hundred feet of lime- 

 stones represent the Lower and Upper Silurian and the Carboniferous, 

 as on the other side of the range. Their area here is limited, and has 

 not been traced to its abutment against the volcanic rocks, which fill 

 the depression to the northward. The range is much flattened and 

 rounded off at this extremity ; and I am inclined to believe that the 

 granitoid nucleus declines so much as to allow of the connection of the 

 limestones of the east and west slopes being exposed between it and the 

 volcanic rocks. At least, the di-ps indicate that such awarj^ed connect- 

 ion once existed ; and I shall not be very far vv'rong in coloring the map 

 according to that supposition. The underlying quartzite (Potsdam 1) 

 was not seen here, but is probably in place, as it appears a few miles 

 farther south. The most northern large caiion of the* range exposes, 

 beneath the limestones, a heavy body of dark micaceous gneiss, with 

 both granite and quartz veins. The local dip is northeasterly ; but the 

 main dip of the metamorphic rocks here is southerly. 



