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Show 1292 REPORT OP THE CHIEF OF ENGINEERS. feet examples of glacial lakes. South of Lake Tahoe extends Lake Valley for fifteen miles as a plain gently rising southward. Its lower end is but a few feet above the lake- surface, and covered with glacial drift modified by water and diversified, particularly on the western side, by debris ridges, the moraines of glaciers which continue to flow into the valley or into the lake long after the main glacier had dried up. " Fallen Leaf Lake glacier.- This lake is bordered on either side by an admirably-marked dibris ridge ( moraines) 300 feet high, 4 miles long, and 1£ to 2 miles apart. These moraines may be traced back to the termination of the rocky ridges that bound the caHon. On the one Bide the moraine lies wholly on the plain, on the other side its upper part lies against the slope of Mount Tallac. Near the lower end of the lake a somewhat obscuro branch ridge comes off from each main ridge, and, curving round, they form an imperfect terminal moraine, through which the outlet of the lake breaks its way. On ascending the canon, the glaciation is very conspicuous, and becomes more and more beautiful at every step. From Soda Springs upward it is the most splendid I have ever seen. In some places the whole rocky bottom of the cation is smooth, polished, and gently undulating, like the surface of a glassy but billowy sea. The glaciation is distinct also up the sides of the canon 1,000 feet above its floor. There can be no doubt, therefore, that a glacier once came down this caftan, filling it 1,000 feet, scooped out Fallen Leaf Lake just where it struck the plain, and changed its angle of slope, and pushed its snont 4 miles ont on the level plain nearly to the present shores of Lake Tahoe, dropping its debris on either side, and thus forming a bed for itself. In its subsequent retreat it seems to have rested its snout some time at the lower end of Fallen Leaf Lake, and accumulated there an imperfect terminal moraine. " Cascade Lake glacier.- On either side of the creek, running ont of this lake from the very border of Lake Tahoe, runs a moraine ridge up to the lake, and thence aloug each side of it np to the rocky points, which terminate the true mountain canon above the head of Cascade Lake. I have never anywhere seen more perfectly- defined moraines. I climbed over the larger western moraine and found that it is partly merged into the eastern moraine of Emerald Bay, to form a medial at least 300 feet high and of great breadth. From the surface of the little lake, the enrving branches of the main moraine, meeting below the lake to form a terminal moraine, are very distinct. At the head of the lake there is a perpendicular cliff, over which the head of the river precipitates itself, forming a very pretty cascade of 100 feet or more. On ascending the canon above the head of the lake for several miles I fonnd everywhere above the lip of the precipice, over the whole floor of the canon, and up the sides 1,000 feet or more, the most perfect glaciation. There cannot be, therefore, the slightest doubt that this is also the pathway of a glacier which once ran into Lake Tahoe. After coming down its steep, rocky bed it precipitated itself over the cliff, scooped out the lake at its foot, and ran on till it bathed its snont in the waters of Lake Tahoe, and probably formed icebergs there. In its subsequent retreat it seems to have dropped more debris in its path, and formed a more perfect terminal moraine than did Fallen Leaf Lake glacier. " Emerald Bay glacier.- All that I have said of Fallen Leaf Lake and Cascade Lake applies almost word for word to Emerald Bay. This beautiful bay, almost a lake, has been formed by a glacier. It is also bounded on either side by moraines, which ruu down to and even project into Lake Tahoe, and may be traced up to the rocky points that form the mouth of the canon at the head of the bay. Its eastern moraine, as already stated, is partly merged into the western moraine of Cascade Lake to form a huge medial moraine. Its western moraine lies partly against a rooky ridge tunning down to Lake Tahoe to form Rubicon Point. At the bead of the bay, as at the head of Cascade Lake, there is a cliff about 100 feet high, over which the river precipitates itself and forms a fine cascade. Over the lip of this cliff and in the bed of the canon above, and np the sides of the cliff- like walls, 1,000 feet or more, the most perfect glaciation is fonnd. The only difference between this glacier and the two preceding is that it ran more deeply into the main lake, and the deposits dropped in its retreat did not rise high enough to cut off its little rock basin from that lake, but exists now only as a shallow har at the mouth of the bay. This bar consists of true moraine matter, i. « ., intermingled bowlders and sand, which may be examined through the exquisitely transparent water almost as perfectly as if no water were present. Some of the bowlders are of large size. One sees from the top of Tallac Peak the whole course of thes* three glaciers, their fouutain amphitheaters, their canon beds, and their lakes inclosed between their moraine arms." Professor Le Conte has fonnd abundant evidence of the former existence of a great glacier in Lake Valley. Bowlders aud pebbles of slate on the north shore of Fallen Leaf Lake can easily be traced to their parent rock in the oafion above the lake. These pebbles have also been traced along the western shores of the great lake beyond S< igar Pino Point to the extreme northwestern shore, nearly thirty miles from their sonrce. The Fallen Leaf Lake glacier was once a tributary to a much greater glaeier that filled Lake Tahoe. Again, Le Conte finds additional evidence of a Lake Tahoe mer de glace in the contrasted character of the northern and southern shores of the lake. The same |