20 NORTH AMERICAN FAUNA. [No. 16, 
but they have cut for themselves deep gorges where they run their 
rapid courses 1,000 feet below the surface, and consequently are use- 
less for purposes of general irrigation. They exert a local influence, it 
is true, since far down in the damp bottoms of the canyons and along 
their cool easterly lower slopes anumber of moisture-loving plants occur 
that are not found elsewhere except about the few and widely scattered 
springs in the forest—serving by contrast to accentuate the general 
aridity. Even the black alpine hemlock, which in the Cascades forms 
so attractive a feature of the upper slopes, is of local occurrence on 
Shasta, where its distribution is interesting as furnishing an index to 
soil moisture. It is associated with the white-bark pine (Pinus albi- 
caulis), which requires less moisture and is the dominant timberline 
tree. In our circuit of the peak we found the range of the white-bark 
pine practically continuous; that of the alpine hemlock discontinuous 
and greatly restricted. .As a rule the hemlock is confined to narrow 
strips along the streams and gulches, or to tongues along the cool east 
sides of buttes and ridges, where the soil, sheltered from the hot after- 
noon sun, is able to retain more moisture than elsewhere. Below the 
alpine hemlocks and occupying the middle belt of the mountain is a 
magnificent forest of Shasta firs; but the humbler vegetation of this 
belt is scanty and irregular. 
From what has been said it is obvious that excessive dryness pre- 
vents many of the characteristic zone species from filling their appro- 
priate belts, restricting them to scattered spots, where, as in the desert, 
succulent vegetation is concentrated about springs and streams. Hence 
Shasta is a poor place to study the broad general facts of zone distri- 
bution, but, as shown later, an admirable place to study detailed effects 
of slope exposure and humidity. 
GLACIAL BASINS. 
As in most parts of the Sierra and many parts of the Cascades, gla- 
cial basins are conspicuous on the higher slopes of the mountain. They 
occupy the deep depressions between the radiating ridges, and their 
terminal moraines are usually clearly defined. In some of the valleys, 
as along the upper part of Squaw Creek, two or three such moraines 
may be found at intervals, marking successive stages in the retreat of 
the glacier. The glacial basins usually contain small streams, at least 
during spring and early summer, and they receive additional moisture 
from the melting snows, which linger long in the shadows of the ridges. 
This moisture permits the growth of a more abundant vegetation than 
occurs elsewhere on Shasta, save only along the streams. The bottoms 
of the basins therefore are usually carpeted with red heather (Bryanthus 
or Phyllodoce empetriformis) and a variety of small plants, the majority 
of which are inconspicuous except when in flower. Among the most 
noticeable of these, each contributing its mite to the general verdure 
of the leather beds, are the dwarf huckleberries, white alpine anten- 
