REVIEWS 95 
most transparent, that of the green less, and that of the yellow 
least. 
IX. Matter dissolved tn the water of the lakes.—With the exception 
of the salt lakes, none of the lacustrine waters contain so much as 
one gram of solid matter per liter, and in five cases only does it 
exceed .3 gram per liter. There are notable variations in the amount 
and kind of dissolved matter depending upon the character of the 
basin, and there are notable variations in the same lake in differ- 
ent seasons, and in different parts during the same season. In the 
summer the warm waters in the upper portions of the lakes are poorer 
than the colder waters below, in some of the dissolved substances, 
especially Ca CO, and SiO,, while in winter the solutions are nearly 
uniform throughout. In general, the lake waters have less solid mat- 
ter in solution than the inflowing rivers, showing that dissolved 
matter is lost in the lakes. ‘This loss is attributed largely to precipita- 
tion, and it seems to be implied that calcareous tufa is of very common 
occurrence. This would hardly hold for the greater number of the 
lakes in the United States. With reference to dissolved gases, the con- 
clusion is reached that the amount of these gases, chiefly CO,, O, and 
N, are independent of pressure, but that they increase with depth 
on account of the lower temperature. The amount of carbonic acid 
gas dissolved far exceeds that of oxygen and nitrogen together, 
whether measured by weight or by volume. Little account is taken of 
other gases. 
X. Geological position and origin.—The classification of lakes in 
general is briefly outlined, and the lakes of France fitted to the classi- 
fication. Two primary classes of lake basins are recognized : (1) Those 
produced by barriers of one sort and another, and (2) rock basins. Of 
the barrier basins there are many types, most of which are represented 
in France. The barriers are of various types as follows: (1) Land- 
sides. Lake basins produced in this way are found in the Alps, the Juras 
and the Pyrenees, but are not numerous. (2) ce. No existing lake in 
France owes its existence to an ice barrier. One extinct lake is so 
classed. (3) Moraines. The moraine of an existing glacier is the 
barrier which gives origin to a single lake,— Lac Long in the Alps. 
Lakes which owe their origin to moraines of extinct glaciers are numer- 
ous and of several classes. Here belong (a) lakes in valleys which 
were occupied by glaciers, the moraine forming a dam at the lower end 
of the lake. Of this class there are several representatives in the Alps, 
