GEOLOGY. 249 
of: the valley. On the retreat of the ice, owing to 
climatal changes, this hollow, unless previously choked up 
with sand and stones, will be filled with water, and form a 
lake. It will be a true rock basin, with ice-worn surfaces 
around its lip, and over its sides and bottom. 
‘ And such is the appearance presented by many a lake 
and tarn in the Highlands of Scotland. One of the largest 
and noblest of the whole—Loch Awe—may be taken as 
an illustrative example.’ 
Nor isitonly the formation of single lakes which can be thus 
accounted for ; a continuous succession of lakes in the direc- 
tion of the movement of the glacier may be thus produced. 
As popular illustrations of the mode of operation I may 
cite the following :— Young boys, and girls too, amuse them- 
selves making what they call ‘ducks and drakes’ by 
throwing flat stones across a placid sheet of water, as 
nearly parallel to the surface of it as they can, causing 
them to skim along and above the water, touching and 
rising again and again, rebounding in ever-diminishing 
bounds till they sink. The same phenomenon may be 
seen on a larger scale in the recochetting of a cannon ball 
fired at a target out at sea; and the same thing may be 
seen in the effects of the wind striking the surface of the 
water in a river, in a lake, or in the sea, for rarely, if ever, 
does it blow horizontally or parallel to the surface of the 
water. Where it impinges it raises a little wavelet, and 
rebounds, but only to strike again a little in advance, again 
and again to rebound, producing a succession of advancing 
elevations and depressions. In another volume entitled 
Forests and Moisture,* T have had occasion to refer to another 
* Forests and Moisture ; or, Effects of Forests on Humidity of Climate. In which 
are given details of ph of vegetation on which the meteorological effects of 
forests affecting the humidity of climate depend,—of the effects of forests on the humi- 
dity of the atmosphere, on the humidity of the ground, on marshes, on the moisture of 
a wide expanse of country, on the local rainfall, and on rivers,—and of the correspon- 
dence between the distribution of the rainfall and of forests,—the measure of corres- 
pondence between the rainfall and that of forests,—the distribution of the rainfall 
dependent on geographical position, determined by the contour of a couotry,—the dis- 
tribution of forests affected by the distribution of the rainfall,—and the local effects of 
forests on the distribution of the rainfall within the forest district.—Edinburgh : Oliver 
and Boyd. London: Simpkin, Marshall, & Co. 1877. 
