564 Proceedings of the Royal Society 
followed the very heavy floods of 24th August, contained more 
colouring matter, exhibited less action with the ordinary liquid 
tests for the inorganic salts, and had a hardness of L4 degree 
only. I have no doubt that this water corresponded in all respects 
very closely with the specimen examined by Mr Dewar. 
Thus, it appears, that the waters of St Mary’s Loch — which, 
with the exception perhaps of those in the primitive districts of Kirk- 
cudbrightshire and Wigtownshire, may be taken as a type of the 
lowland lochs at large — differ from the waters of the Highland 
lakes in containing more solid matter, a little more saline matter, 
and decidedly more colouring organic matter, and in being consi- 
derably harder, though really belonging to the “ soft ” waters too. 
Another difference is that they vary more with the season, the salts 
becoming rather more abundant in long dry weather, and the 
colouring matter clearly abounding more during and after floods. 
Finally, a remarkable difference in property, to be discussed by- 
and-by, is, that unlike the waters of the Highland lochs, that of 
St Mary’s Loch does not erode lead. But first let me say a word 
or two about the Yarrow Water, by which this lake discharges 
itself. 
The Yarrow, before uniting with the Ettrick, wdnds for 14 miles 
through a narrow, bare, chiefly pastoral vale, bounded by gently 
sloping hills. It is joined in this course by twenty-two tributaries, 
of which only three or four are considerable streamlets, the others 
being mostly rills, apt to be dried up, or nearly so, in dry weather. 
The waters of the chief tributaries contain in the dry season more 
salts than the main stream itself, but very much less colouring 
matter, two of them, indeed, none at all appreciable even in a 16- 
inch tube. The channel of the Yarrow is wide and stony, and the 
stream shallow, and for the most part turbulent. In the 14 miles 
it falls 220 feet. Its banks present very few human habitations. 
These circumstances are favourable to the gradual diminution of 
organic impregnations, partly through the decomposing influence 
of fresh earthy salts added here and there by little tributaries, 
partly by the slow oxidation, to which Liebig gave the name of 
“ Eremacausis,” — “ quiet” or “ slow burning.” My attention was 
turned very long ago, before the publication of Liebig’s views on 
this subject, to the rapidity with which, by natural processes, 
