42 



NORTH AMERICAN FAUNA. 



[N-n. 16. 



on a biirrou ])umice slo])e to 7,000 lect, where, sparingly mixed with 

 alpiue hemlocks, they meet tlie iii)]>er limit of Sliasta liis and silver 

 pines. 



]Jlack Alpine nE:\Li.O('K {'rsinia mrrtensland'^ ). — lUit the wliite- 

 bark pine, although the dominant and most widely distributed tree of 

 the up])er timber belt, is not the only tree, for in i)laees it is mixed 

 with or re])laced by the black alpine hemlock. Shasta is a Yevy dry 

 mountain, and yet the white-bark pine thrives on its driest slopes and 

 grows among the bare, naked blocks of lava where tree life seems 

 irai)ossible. The hemlock re(iuires more moisture, and therefore is at a 

 decided disadvantage. It never reaches as high as ri)nis <il]>!('((uJis 

 and attains its best development along the lower border of the Hud- 



FlG. 24. — r.lack alpine lieiiilocks mar Scjuaw ('i 



sonian /one, where it occurs iu disconnected sheltered localities — 

 usually in canyons or on the shady east or northeast sides of buttes or 

 ridges, where there is more moisture than on the exposed slo])es. Since 

 these shady easterly slopes are always cold, tlie hemlocks that occupy 



'This is the species heretofore coiiiinoiily laiowii as Tsin/a jxtltoni ov Ti^mia patio- 

 niana. It lias been recently discox-crod lliat the name Tniuja mcricnsiana, commonly 

 :ij)]ilie(l to the racilif lowland hemlock, wiis first <;iveii to the jjrcseut aljiiiie 8])ccies, 

 iiecessitatinj; a most nnhajiiiy change oi" name. Fortunately, however, the common 

 Knglish names of the two ami Ihcir widely difl'erent /one ranges — one restricted to 

 the low Transition licit ncai- the inast, the other to the high lludsoniau zone on the 

 lof'tii'st mountains — may ]ire\ciit the confusion that otherwise would result from the 

 change of name. 



