that when the affluents of such lakes are locked in the icy fetters of winter, much less suspended matter is carried into them than in summer, when all the sub-glacial streams are in active operation.

Professor Le Conte goes into this subject (as he later does into the subject of the color of Lake Tahoe) somewhat exhaustively in a purely scientific manner and in too great length for the purposes of this chapter, hence the scientific or curious reader is referred to the original articles for further information and discussion.

Color of the Waters of Lake Tahoe.  One of the most striking features of this charming mountain Lake is the beautiful hues presented by its pellucid waters.  On a calm, clear, sunny day, wherever the depth is not less than from fifty to sixty meters, to an observer floating above its surface, the water assumes various shades of blue; from a brilliant Cyan blue (greenish-blue) to the most magnificent ultramarine blue or deep indigo blue.  The shades of blue increasing in darkness in the order of the colors of the solar spectrum, are as follows:  Cyan-blue (greenish blue), Prussian-blue, Cobalt-blue, genuine ultramarine-blue, and artificial ultramarine-blue (violet blue).  While traversing one portion of the Lake in a steamer, a lady endowed with a remarkable natural appreciation and discrimination of shades of color declared that the exact tint of the water at this point was “Marie-Louise blue.”

The waters of this Lake exhibit the most brilliant blueness in the deep portions, which are remote from the fouling influences of the sediment-bearing affluents, and the washings of the shores.  On a bright and calm day, when viewed in the distance, it had the ultramarine hue; but when looked fair down upon, it was of almost inky blackness—­a solid dark blue qualified by a trace of purple or violet.  Under these favorable conditions, the appearance presented was not unlike that of the liquid in a vast natural dyeing-vat.

A clouded state of the sky, as was to be expected, produced the well-known effects due to the diminished intensity of light; the shades of blue became darker, and, in extreme cases, almost black-blue.  According to our observations, the obscurations of the sky by the interposition of clouds produced no other modifications of tints than those due to a diminution of luminosity.

In places where the depth is comparatively small and the bottom is visibly white, the water assumes various shades of green; from a delicate apple-green to the most exquisite emerald-green.  Near the southern and western shores of the Lake, the white, sandy bottom brings out the green tints very strikingly.  In the charming cul-de-sac called “Emerald Bay,” it is remarkably conspicuous and exquisitely beautiful.  In places where the stratum of water covering white portions of the bottom is only a few meters in thickness,