20 NORTH AMERICAN FAIXA. 



[NO. 16. 



but tliey Lave cut for themselves deep gorges where they run their 

 rapid courses 1,000 feet l)eh)M' the surfa(;e, and consecpieiitly are use- 

 less for purposes of general irrigation. They exert a local influence, it 

 is true, since far down in tlie damp bottoms of the canyons and along 

 their cool easterly lower slopes a number 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 liendock, which in the Cascades forms 

 so attractive a feature of the upper sloi)es, 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- 

 caiilis), which requires less moisture and is the dominant timbeiiine 

 tree. In our circuit of the peak we found the range of the white-bark 

 pine ])ractically 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 occui)ying 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 i)lace 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 IJASINS. 



As in most i»arts of the Sierra and many parts of the Cascades, gla- 

 cial l)asins are conspicuous on the higher slopes of the mountiiin. Tliey 

 occupy the deep depressions between the radiating ridges, and their 

 terminal moraines are usually clearly defined. In some of the valleys, 

 as along tlu; ui)]»er ])art of Sipiaw Creek, two or three such moraines 

 may be found at intervals, marking su(;cessive 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, whi(;h linger long in the shadows of the lidges. 

 This moisture ])ermits 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 heatlier {Ih-yanthns 

 or rinjUodocc oiipctrifonnis) and a variety of small plains, the majority 

 of which arc inconspicuous except when in llower. Among the most 

 noticeable of these, each contributing its mite to the general verdure 

 of til*' hrafln r Ix'ds, are the dwarf huckleberries, white aljnne anteu- 



