June 27.--We continued our route over the high and steep hills of the same great ridge. At eight miles' distance, we reached an eminence where the Indians have raised a conical mound of stone six or eight feet high. From this spot we have a commanding view of the surrounding mountains, which so completely enclose us, that, although we have once passed them, we should despair of ever escaping from them without the assistance of the Indians; but our guides traverse this trackless region with a kind of instinctive sagacity. They never hesitate; they are never embarrassed; yet so undeviating is their step, that, wherever the snow has disappeared for even a hundred paces, we find the summer road. With their aid, the snow is scarcely a disadvantage; for although we are often obliged to slide down, yet the fallen timber and the rocks, which are now covered up, were much more troublesome when we passed in the autumn. NOTE. A later traveller through this region writes, "The mountains are indeed _rocky_. They are rocks heaped upon rocks, with no vegetation, excepting a few cedars growing out of the crevices near their base. Their tops are covered with perpetual snow. The main ridge of the mountains is of _gneiss_ rock; yet, to-day, parallel ridges of a rock, nearly allied to _basalt_, have abounded. These ridges appear to be volcanic, forced up in _dikes_ at different distances from each other, running from east-north-east to west-south-west. The strata are mostly vertical; but some are a little dipped to the south. "Our encampment was near a small stream which runs through a volcanic chasm, which is more than a hundred feet deep, with perpendicular sides. Here was a passage made for the _water_ by _fire_." THE PARTY AGREE TO SEPARATE. July 3, 1806.--It was agreed here that the expedition should be divided, to unite again at the confluence of the Missouri and the Yellowstone. The separation took place near the point where Clarke's River is crossed by the forty-seventh parallel of latitude. Capt. Lewis, with nine men, was to cross the mountains in a direction as nearly due east as possible, expecting to find some tributary of the Missouri, by following which he might reach that river, and by it retrace his way homeward. Capt. Clarke, with the remainder of the party, was to seek the head waters of the Yellowstone, and follow that stream to the proposed place of re-union.