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of Edinburgh , Session 1871 - 72 . 
me finish what may be said of the physical characters of the loch, 
by noticing one not yet adverted to. Visitors in the dry season, 
when the waters of the lake are somewhat shrunk, have been 
much struck with the beauty of its border,—its “ silver strand.” 
This is owing to a uniform beach of crowded, chiefly angular, or 
partially rounded, light-grey coloured stones. The colour, however, 
is not their own, but belongs to a generally dense covering of a dried- 
up matter, composed of a multitude of various diatoms entangled in 
the delicate lines of a finely fibrous conferva. In the fresh state 
this investing matter is dark greenish-brown, close, and slimy. The 
stones, therefore, give the loch, even in its shallows, a disagreeable, 
dark, deep appearance, abruptly defined by the water’s edge. But 
all of them out of water acquire, in drying, a light grey or greyish - 
white hue. Every scientific visitor has observed, and some have 
carefully examined, these stones and their covering. But, so far 
as I am aware, no one has noted their full significance; of which 
more presently, when I come to speak of the Yarrow. 
The water of the loch, though it is coloured, is a pure water,— 
in the sense that it contains very little solid matter in solution. 
It has been repeatedly analysed, and found to contain rather less 
than a 20,000th part of total solids. Mr Dewar, the latest analyst, 
I believe, found a 22,440th,—of which the inorganic salts consti¬ 
tuted two-thirds [a 37,000th], and the organic matter one-third [a 
55,500th]. The chief inorganic salts are the same as in the mica- 
slate streams and lochs of the Highlands, and much in the same 
proportion to one another. The hardness of the water was found 
by Mr Dewar to be 1'30 degrees by the soap-test, or nearly twice 
that of Loch Lomond surface water. Other chemists have found 
more solids, some less. My own results, with water collected on 
13th June, show more saline, and rather less organic, matter; 
which is no more than might have been anticipated from the long- 
antecedent very dry weather. I found the solid contents dried at 
about 300° F. to be a 15,000th of the water; one-fourth of this 
was destroyed by slow incineration at a low red heat; and the hard¬ 
ness was 2-0 degrees of Clark’s soap-test scale,—which is about the 
fourth part of that of the present Edinburgh water supply. Water 
collected three months later, on 8th September, after ten days of 
complete drought, which, after a few days of showery weather, 
