The weather was calm and clear while the detachment remained on the peak; but we were surprised to observe the air in every direction filled with such clouds of grasshoppers, as partially to obscure the day. They had been seen in vast numbers about { 221} all the higher parts of the mountain, and many had fallen upon the snow and perished. It is, perhaps, difficult to assign the cause which induces these insects to ascend to those highly elevated regions of the atmosphere. Possibly they may have undertaken migrations to some remote district; but there appears not the least uniformity in the direction of their movements.[7] They extended upwards from the summit of the mountain to the utmost limit of vision; and as the sun shown brightly, they could be seen by the glittering of their wings, at a very considerable distance.
About all the woodless parts of the mountain, and particularly on the summit, numerous tracks were seen, resembling those of the common deer, but most probably have been those of the animal called the big horn. The skulls and horns of these animals we had repeatedly seen near the licks and saline springs at the foot of the mountain, but they are known to resort principally about the most elevated and inaccessible places.
The party remained on the summit only about half an hour; in this time the mercury fell to 42°, the thermometer hanging against the side of a rock, which in all the early part of the day had been exposed to the direct rays of the sun. At the encampment of the main body in the plains, a corresponding thermometer stood in the middle of the day at 96°, and did not fall below 80° until a late hour in the evening.
Great uniformity was observed in the character of the rock about all the upper part of the mountain. { 222} It is a compact, indestructible aggregate of quartz and felspar, with a little hornblende, in very small particles. Its fracture is fine, granular, or even; and the rock exhibits a tendency to divide when broken into long, somewhat splintery fragments. It is of a yellowish brown colour, which does not perceptibly change by long exposure to the air. It is undoubtedly owing to the close texture and the impenetrable firmness of this rock that so few lichens are found upon it. For the same reason it is little subject to disintegration by the action of frost. It is not improbable that the splintery fragments, which occur in such quantities on all the higher parts of the peak, may owe their present form to the agency of lightning. No other cause seems adequate to the production of so great an effect.