42 NORTH AMERICAN FAUNA, [x0 16, 
on a barren pumice slope to 7,000 feet, where, sparingly mixed with 
alpine hemlocks, they meet the npper limit of Shasta firs and silver 
pines. 
Buack ALPINE HEMLOCK (Tsuga aertensiane!).—But the white- 
bark pine, although the dominant and most widely distributed tree of 
the upper timber belt, is not the only tree, for in places it is mixed 
with or replaced ly the black alpine hemlock. Shasta is a very 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 
impossible. The hemlock requires more moisture, and therefore is at a 
decided disadvantage. It never reaches as high as Pinus albicaulis 
and attains its best development along the lower border of the Hud- 
Fie, 24 —Blavk alpine hemlocks near Syuaw Creek. 
sonian zone, where it occurs in disconnected sheltered localities— 
usually in canyons or on the shady east or northeast sides of buttes or 
ridves, where there is more moisture than on the exposed slopes. Since 
these shady easterly slopes are always cold, the hemlocks that occupy 
'This is the species frepetotlire eonmronlig known as Tange pattoni or Piagia patto- 
niana. It has lwen recently discovered that the name Tsuga mertensiana, commonly 
applied to the Pacific lowland hemlock, was first given to the present alpine species, 
necessitating a most unhappy change of name. Fortunately, however, the common 
English names of the two and their widely different zone ranges—one restricted to 
the low Transition belt near the coast, the other to the high Hudsonian zone on the 
loftiest monutains—may prevent the confusion that otherwise would result from the 
change of name. 
