c.  Passage of slate into granite.  From the commencement of the rocky canyon at the head of Fallen Leaf Lake, and up for about two miles, the canyon walls and bed are composed of slate.  The slate, however, becomes more and more metamorphic as we go up, until it passes into what much resembles trap.  In some places it looks like diorite and in others like porphyry.  I saw no evidence, however, of any outburst.  This latter rock passes somewhat more rapidly into granite at Glen Alpine Springs.  From this point the canyon bed and lower walls are granite, but the highest peaks are still a dark, splintery, metamorphic slate.  The glacial erosion has here cut through the slate and bitten deep into the underlying granite.  The passage from slate through porphyritic diorite into granite may, I think, be best explained by the increasing degree of metamorphism, and at the same time a change of the original sediments at this point; granite being the last term of metamorphism of pure clays, or clayey sandstones, while bedded diorites are similarly formed from ferruginous and calcareous slates.  Just at the junction of the harder and tougher granite with the softer and more jointed slates, occur, as might be expected, cascades in the river.  It is probable that the cascades at the head of Cascade Lake and Emerald Bay mark, also, the junction of the granite with the slate—­only the junction here is covered with debris.  Just at the same junction, in Fallen Leaf Lake Canyon (Glen Alpine Basin), burst out the waters of Glen Alpine Springs, highly charged with bicarbonates of iron and soda.

d.  Glacial Deltas.  I have stated that the moraines of Cascade Lake and Emerald Bay glaciers run down to the margin of Lake Tahoe.  An examination of this portion of the Lake shore shows that they run far into the Lake—­that the Lake has been filled in, two or three miles, by glacial debris.  On the eastern margin of Lake Tahoe, the water, close along the shore, is comparatively shallow, the shore rocky, and along the shore-line, above and below the water, are scattered great bowlders, probably dropped by the main glacier.  But on the west margin of the Lake the shoreline is composed wholly of moraine matter, the water very deep close to shore, and the bottom composed of precisely similar moraine matter.  In rowing along the shore, I found that the exquisite ultramarine blue of the deep water extends to within 100 to 150 feet of the shore-line.  At this distance, the bottom could barely be seen.  Judging from the experiments of my brother, Professor John Le Conte, according to which a white object could be seen at a depth of 115 feet, I suppose the depth along the line of junction of the ultramarine blue and the emerald green water is at least 100 feet.  The slope of the bottom is, therefore, nearly, or quite, 45 degrees.  It seems, in fact, a direct continuation beneath the water of the