Looking back over the snow we had crossed, two well-characterized features on its surface could be distinguished : these were large areas with a gray tint, caused by a covering of dust. This dust comes from the southern faces of the Pinnacle pass cliffs, and is’ blown over the crest of the ridge and scattered far and wide over the snow-fields toward the north. Should the dust-covered areas become buried beneath fresh snow, it is evident that the strata of snow would be separated by thin layers of darker color. This is what has happened many times, as we could see by looking down into the crevasses. In one deep gulf I counted five distinct strata of clear white snow, separated by narrow dust-bands. In other instances there are twenty or more such strata visible. Each layer is evidently the record of a snowstorm, while the dust-bands indicate intervals of fine weather. The strata of snow exposed to view in the crevasses, after being greatly compressed, are usually from ten to fifteen feet thick, but in one instance exceeded fifty feet. If we assume that each layer represents a winter’s snow, and that compression has reduced each stratum to a third of its original thickness (and probably the compression has been greater than this), it is evident that the fresh snows must sometimes reach the depth of from 50 to 150 feet. Toiling on up the snow-slope, we had to wind in and out among deep crevasses, sometimes crossing them by narrow snow-bridges, and again jumping them and plunging our alpenstocks deep in the snow when we reached the farther side. After many windings we reached the summit of the Pinnacle-pass cliffs. The crest-line is formed of an outcrop of conglomerate composed of sand and pebbles, in one layer of which I found large quantities of mussel shells standing in the position in which the creatures lived. The present elevation of this ancient sea-bottom is 5,000 feet. The strata incline northward at angles of 30 to 40. All of the northern slope of the ridge is deeply covered with snow, and the rock only appears along the immediate crest. There are, in fact, two crests, as is common with many mountain ridges in this rigion, one of rock and the second of snow ; the snow crest, which is usually the higher, is parallel to the rock crest and a few rods north of it. In the valley between the two ridges we found secure footing, and ascended with ease to the highest point on the cliffs. Looking over the southern or rocky crest, we found a sheer descent of about 1,500 feet to the snow-fields below.