HOLMES] GEOLOGY OF SEPULCHEE MOUNTAIN. 15 



and glacial, covers the whole face of the country for a number of miles 

 east of Mount Evarts. Down toward the canon of the Yellowstone 

 ledges of columnar basalt outcrop along the deei) gulches. 



SEPULCHRE MOUNTAIN. 



Why this mountain received such a melancholy appellation I have not 

 been able to discover. So far as 1 know it, the most important thing 

 buried beneath its dark mass is the secret of its structure. It is possi- 

 ble that the form has suggested the name. In shape it is a rudely rect- 

 angular mass with pretty even and rather gentle slopes below, and 

 steep walls above, which culminate in an elongated and flattened crest. 

 Topographically it is almost isolated. The north base is washed by the 

 Yellowstone River, the east by Gardiner Elver, the west by Cache 

 Creek, and the south by the West Gardiner. Geologically, also, it stands 

 alone. It is a mountain, built up of recent volcanic ejecta, in a broad 

 depressed space between two sedimentary mountains, Mount Evarts and 

 Electric Peak. 



The former has a great wall, facing Sepulchre Mountain, on the east, 

 composed of Cretaceous strata which dip to the north at a gentle angle. 

 The latter has a similar wall which overlooks it on the west side. To 

 all appearances these strata originally connected across, having doubt- 

 less a uniform slope toward the line of the Yellowstone fault. What 

 causes conspired to plane down the space between these walls I know 

 not, but that such a planing down occurred, and that subsequent vol- 

 canic ejecta built up a mountain on the depressed space, are patent facts. 



On the occasion of each of my visits to the summit of Mount Evarts 

 the weathfr was such as to prevent the sketching of the east face of 

 Sepulchre Mountain. On the first visit the broad, undulating slope 

 that rises gradually from Gardiner Eivei toward the steeper crest could 

 be indistinctly made out, and the white and parti-colored mass of the 

 ]M am moth Hot Springs appeared like a fragment of a glacier in the 

 midst of the mountain. Forest and pasture lands occupy nearly equal 

 portions of the surface, and the exposures of geologic formations are in- 

 frequent save toward the summit. The greater part of the whole sur- 

 face has a remarkably perplexing topography, the hot-spring deposits 

 and the very numerous land slides having produced thousands of de- 

 pressions and elevations that are totally without system in their arrange- 

 ment. 



There is a very general distribution of drift material over the lower 

 sloi^es, the origin of which is rather puzzling. As high up as the springs, 

 and even to the divide that separates the upper valley of the West Fork 

 from the main valley below, there are remnants of drift-covered terraces. 

 Some of these steps are the result of hot-spring deposits, but others are 

 undoubtedly due to the action of water or ice. 



The great trough-like valley of the Gardiner is undoubtedly due to 

 erosion, and has probably been of rapid formation, since as soon as the 

 river had penetrated the sheet of rhyolite upon which it was first super- 

 imposed, and the firmer strata of the Upper Cretaceous formations, the 

 cutting would necessarily be very rapid through the less cojHpact for- 

 mations of the Middle Cretaceous, and what is more, by a ])rocess of 

 undermining, the valley being monoclinal, the bed of the stream would 

 descend with the dip of the rocks, and hence have a tendency to movB 

 from the west to the east. The whole series of flood planes would nat- 

 urally be left unchanged on the west side, excepting as they happened 

 to be destroyed by the very meager lateral drainage or by slides. 



