24 NORTH AMERICAN FAUNA. [xo. 16, 
The banks of the more permanent streamlets are so well supplied 
with moisture that the heather and other plants, often mixed with 
alpine mosses,! form a sod which, growing thicker each year, gradually 
comes to overhang and finally bridge the swiftly running water. Even 
away from these sod bridges, which for long distances completely hide 
the water, the space between the constantly protruding banks is so 
narrow that only the middle part of the stream can be seen. 
The icy rivulets abound in cascades, miniature waterfalls, and crys- 
tal pools, bordered by overhanging banks of moss, heather, and dwarf 
alpine laurel, and adorned by the waving heads of the scarlet painted 
Fic. 11.—Miniature cascade on upper Squaw Creek, frequented by water shrews and ouzels. 
cups and cream-colored parnassias. They are ideal homes for the water 
ouzel (Cinclus mericunus), the large water shrew (Veosorer navigator), 
and the mountain vole (Microtus mordar), The latter avimal is par- 
ticularly abundant, and its dark burrows, almost hidden among the 
plants, may be found opening out on the vertical overhanging banks 
only a few inches above the water, so that whenever the occupants 
come out they may plunge in the icy stream before proceeding on their 
journey. Minks occur lower down along the streams, and still lower, 
otters. 
1The prevailing moss on the banks of the alpine streams is Lulacomnium androgy- 
num. 
