BIOLOGICAL RECONNOISSANCE AT FLATHEAD LAKE. | 164 
lower end. They were all dead, and no doubt were washed in from the 
fearby marshes. 
Sphaerium partumeium, Say. A single dead specimen was taken 
along shore at the lower end. The statement made for the preceding 
srecies will no doubt apply to this. 
Pyramidula strigosa var. cooperi, W. G. B. This land species was 
taken abundantly by Mr. Silloway, who reported it in great quantities. 
during the wet month of June. It is interesting te note that it does not 
seem to be mixed with P. solitaria, so abundant on the opposite side of 
the Mission range. 
The annual rise and fall of the lake does not seem to be more than 
a few feet. The area draineu is almost entirely wooded. The snow is 
therefore held back in spring by the timber, which prevents the sun 
from taking it off rapidly. The only water of any importance entering 
lake is the river, which enters the bay toward the upper end as previ- 
ously mentioned. On the east one small creek and several rivulets carry 
a few second feet of water. There are no streams worth mentioning. 
coming from the Mission range into the lake. The entire shore along 
the Swan range at the upper end is springy. A few inches below the 
surface at almost any point reveals cold water, seepage from the hills, 
no doubt. The amount of water brought to the lake from this source is 
not known. The river at the inlet and outlet have not as yet been 
measured, and the flow cannot therefore be given. 
Air currents in the region of Swan lake are pronounced, and merit 
notice. Lying in a cradle between two mountain ranges, its surface must 
be stirred by every mountain breeze. As has been mentioned, the higher 
slopes of both ranges are south of the lake. In summer these higher sum- 
mits contain the greater portion of snow, while the peaks nearer the 
lake are mostly bare, save on the north and east. During the day these 
rock summits become heated, the warm air rising as the rocks become 
more and more affected by the sun. A current of air is therefore put in 
motion up the lake. This is usually felt during the day in summer. At 
dusk, after the sun has set, the reverse takes place. The rocks along 
the mountain ranges which during the day have been warm now cool 
rapidly. The cool air is heavy, and flows down the mountain slopes 
toward the center of the valley. Down this it moves. As it crosses 
the lake from the upper to the lower end its movement may be followed 
by the ripples on the surface. Occasionally this is intensified by a 
breeze, which may be occasioned in the same manner by extremes of heat, 
but which probably has some other origin. The result is a strong wind, 
perhaps sufficient to be called a gale, which piles up the water at the 
narow outlet into waves of much force for so small a body of water. 
The lake is free from driftwood. The currents just mentined no 
doubt carry all the drift down lake to the outlet. From this place it may 
easily pass down the river and on to Flathead lake. 
From its beautiful location in the heart of the mountains Swan lake 
will no doubt become a resort for those who wish a rest from mental 
labors. It is primitively wild. Game abounds. The lake is large 
enough for extensive boating with small craft. The waters are clear 
