HOLMES.] VALLEY OF GAEDINER RIVER, 29 



interesting chapter in the history of these springs. They existed before 

 the valleys of Gardiner Elver and the Yellowstone were laid out, and 

 built their heavy sheets of deposit upon the level lioor of the unbroken 

 sheet of rhyolite that bridged the future valley. As erosion went on 

 and the bed of the river sank, the springs sank and have followed step 

 by step until now they issue from the hills, a thousand feet below their 

 old level. The great series of terraces that grow less distinct as we 

 ascend from the river attest the truthfulness of this conclusion. The 

 geyser and hot spring action has been spoken of frequently as the last 

 stage of the great volcanic activity of the later Tertiary age. Here we 

 trace the hot-spring terraces far back as so many links that connect the 

 far-distant past with the present without a break. 



In Plate XV, I give an outhne drawing representing the main features 

 of the plateau border region as seen from the eastern flank of Quadrant 

 Mountain, in the East Gallatin Eange. In the middle part of the pict- 

 ure we have a glimpse of the lower valley of the Gardiner. In the fore- 

 ground and on the right hand are the upper valleys of the Gardiner. To 

 the right of the center is Bunsen Peak, a conical mountain (a) which ovre- 

 looks the springs on the south. At the right, beyond, are the rounded 

 forms of the northern part of the Washburn Eange, and beyond this and 

 extending across the picture to the left, the Yellowstone Valley, with 

 the Yellowstone Eange rising to its distant crest on the north. The 

 dotted line marked b indicates the location of the mouth of Gardi- 

 ner's Eiver, which is at an elevation of 5,500 feet. The letters d, /, 

 and h indicate the extreme head or heads of the lower valley. At h 

 the West Fork descends in a cascade over the edge of the rhyolite high- 

 land. At / the middle or main Gardiner makes a corresponding de- 

 scent, and at d we have the falls of the East Fork. The flat mass m 

 with the steep wall fronting us is Mount Evarts, m' being the highest 

 point, 2,200 feet above the river, and the northern termination of the 

 sheet of rhyolite. Beneath, forming the cliff', are the Cretaceous shales. 

 At the head of the valley, between the West and Middle Forks, is 

 Bunsen Peak, the bulk of which is composed of a reddish or pinkish 

 rhyolite. I was prevented from giving this mountain its proper amount 

 of attention, and in consequence am quite unable to explain its occur- 

 rence at such a place. I am inclined to the opinion, however, that it 

 can hardly be a relic of a former plateau of corresponding height, as 

 there are no other remnants of equal height, and the amount of erosion 

 required to reduce the whole of the plateau so many hundreds of feefe-is 

 greater than the local drainings could have accomplished. It more 

 probably marks the site of some center of eruption, where the accumu- 

 lations of the rhyolite lavas were unusually great. The fact that the 

 rhyolite appears so much deeper beneath the general surface here than 

 at other points about the valley below, rather tends to confirm such a 

 conclusion. According to the testimony of Dr. Hay den, who visited this 

 mountain in 1871, the summit is capped with fragmentary basaltic ma- 

 terial. Mr. Gannett brought away, at the time of his visit in 1878, a 

 small fragment of hornblendic trachyte, which is identical with the frag- 

 mentary materials comprising the breccias of Sepulchre Mountain and 

 Mount Washburne. To the left of this mountain and on this side of the 

 deep valley of Gardiner Eiver is the long ridge or narrow plateau n 

 which has already been described as having a capping of hot-spring 

 limestone with underlying rhyolites. To the left of this, and on the 

 opposite side of Wagon-road Pass I is the rounded rhyolite hill n', 

 in the sides of which the Jurassic strata outcrop. To the left of this 

 still we have the spurs of Sepulchre Mountain j, which have a capping 



