1038 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [2] 
caused it to fall about 6 inches lower than its outlet to the sea. The 
fresh-water layer was therefore evaporated so that the surface water 
had a salt taste. This condition was favorable in the respect that it 
had given the young oysters swarming about an opportunity to come up 
into the uppermost layer of water, where they had found points of con- 
tact on the branches of our common dog rose, Rosa canina L., which, 
being cut off, were accidentally thrown into the water. This was for 
me a hint as to how the gathering of young oysters in this basin ought 
to be managed. 
The lake is surrounded on three sides by steep walls of rock 300 to 
400 feet high, and only on the western side facing toward the open sea 
does the middle portion of the mountain slope on both sides down to the 
level of thelake. Through the southeastern depression, when the basin 
is full, fresh water flows out into the sea, while on the contrary during 
westerly storms sea-water presses in more easily through the north- 
western depression, the bottom of which, however, lies nearly one-half 
foot higher than the southeastern. 
A couple of fathoms from the shores the lake has nearly everywhere 
a depth of 6 meters, and slopes therefrom uniformly down towards the 
middle, where the depth is nearly 12 meters. In summer great masses 
of floating conferve are found crowded together both on the surface 
and in the deeper strata of water. This conferva, the only aquatic 
plant in the lake, according to the determination of our algologist, N. 
Willes, is Cladophora crispata (Roth) Kuts. 
In spring, when it begins to sprout, it is bright green, and develops, 
by the influence of the sun, a quantity of oxygen in the form of small 
bladders, w hich collect in masses in the closely entangled web which 
results from the extraordinary branching of this species. Through this 
quantity of air-bladders the cohering mass becomes so much lighter 
than the water that it frees itself from the bottom and rises toward the 
surface, where, little by little, it becomes darker—brownish—and at last 
quite black, whereupon it breaks up into minute fragments which fall 
to the bottom in the form of the finest dust, and communicate to it a 
jet black color. What part this black bottom-color plays in the singu- 
lar thermal conditions of this lake I will attempt to show farther on. 
Upon and in these masses of conferve live two species of gastropods 
both belonging to the genus Rissoa and three or four Acephale of which 
especially a dwar fish form of Cardiwm edule is exceedingly numerous. 
The shells of these three species are black because of the fine conferve 
dust mentioned, but by, being transferred to sea-water, which is free 
from this black powder, they become gradually lighter and finally 
altogether white. At the same time, however, the black color has so 
penetrated into the shelis that they cannot be made much lighter by 
rubbing. The young oysters of from one to two inches diameter always 
have black-striped shells, which can hardly be explained in any other 
way than that the black particles of conferve have been taken up with 
