56t> Proceedings of the Royal Society 
Sundhope, which, too, I could not examine. Other trifling rills, 
almost dried up, join between the Douglas Burn and Yarrow kirk, 
seven miles from the outlet of the lake. This point was a good 
one for studying the joint effect of atmospheric exposure through 
constant agitation, and of the influx of several brooks, all probably 
containing more salts than the main stream itself. Here I found 
that the soap-test indicated a further increase of hardness to 3‘0 
degrees, and that the yellow colour in a 16-inch tube was still 
further reduced, but not much. 
In the next three miles and a half there are six little tributaries, 
all at the time of my visit insignificant, and some quite dried up, 
till we arrive at the Lewenshope Burn, which drains from the 
north a considerable stretch of the Minchmoor range, described to 
me as generally stony hills, without much peat. This water pos¬ 
sessed 6'5 degrees of hardness, and so little colour that it was 
barely appreciable in a 16-inch tube. In the remainder of its 
course the Yarrow is joined by five more rills, either almost dried 
up when I was there, or appropriated in a great measure for the 
supply of mansions. Four hundred yards above its junction with 
the Ettrick, I found its water to possess, as at Yarrow kirk, seven 
miles higher up, 3'0 degrees of hardness, so that the comparatively 
saline water of the Lewenshope had not materially increased the 
salts of the Yarrow. But the colour was still more reduced, so as 
to be very faint indeed, equally so with the colour of the water of 
Loch Lomond. 
Thus the principal loss of colour takes place in the first mile 
and a half of the river’s course ; but there was also a very appreci¬ 
able additional improvement in the longer course below, and the 
final result was a nearly total removal of colour. 
To what is this change owing? Does it depend entirely on the 
intermixture of earthy salts from the tributaries, and on erema- 
causis ? I apprehend that these causes will scarcely account for 
the great change effected in the first mile and a half. There may 
even be a doubt whether peat-extract is particularly subject to the 
process of eremacausis. It is well known to be a preservative of 
organic matters, which it could scarcely be were it very subject to 
decay itself; and I find that a solution of it without any saline 
matter, has undergone no change in a warm room, in a half-filled 
