PRESIDENT S ADDRESS. 
It) I 
tidal communication with the sea. I say daily tidal com- 
munication, because there are bodies of water which are 
in communication with the sea at some periods, the fauna 
of which includes brackish water forms ; and yet, from 
their general characteristics, these are fresh water lakes. 
e.g . — The lake of Oued-Tindja is a large lake communicating 
by a short stream with the lake of Bizerta ; it overflows 
towards the sea in the winter season, and in the summer the 
level falls and the tide rushes up, carrying the salt water 
with it. There are also lagoons of a similar kind in the Island 
of Trinidad. 
Lakes may be divided into three kinds : — 
1. Lakes proper, in which the water is deep enough to 
prevent the growth of aquatic plants on the bottom. 
2. Ponds which are so shallow that plants may take root 
on the bottom. 
3. Marshes, which are ponds almost tilled with vegetation. 
There arc also subterranean lakes, hot springs, and irrigation 
pools, which hardly come under such an enumeration ; and 
further, in a study of Limnobiologv, running water cannot 
be entirely neglected, as numerous organisms which inhabit 
stagnant water also occur in rivers. 
Lake basins may be formed in one or more of several ways : 
1. By the movements of the earth’s crust. 
2. By irregularities in the deposits of sedimentary rocks 
prior to the elevation of the land. 
3. By erosion, through wind, water, or ice. 
4. By the blocking of the channel of a stream — by land- 
slip, lava-stream, etc. 
5: A portion of the sea may be cut oft to form an inland 
lake. 
As to the origin of the Broads, I need only refer to 
Mr. Harmer’s admirable account published in Mr. Dutt’s 
book. 
