

THE SYLVA OF MONTANA. 419 
and Hell Gate valleys, forming the lower half of the east 
side of the basin, where there is, probably, a s pajdersiely dry 
and warm summer. 
Acer glabrum (and var. tripartitum), Betula occidentalis, 
Alnus rubra? Abies Douglassii and Crategus rivularis grow 
throughout but thrive most at the west base of the Coeur 
Alene Mountains, where there is much more rain and hot- 
ter summers (being 2000 feet lower in elevation). 
Populus balsamifera and Pinus contorta are almost equally 
wide-spread ; they are probably finest on the east slope of the 
Cour d’Aleiie Range, where there is a comparatively rainy 
and cold climate which also favors the variety of Abies 
grandis, called amabilis. 
opulus tremuloides and Juniperus Virginiana are so 
scantily distributed that no part of the mountains seems to 
suit them well, though found at intervals in gravelly soil 
where there is not much shade. 
Larix occidentalis is mostly limited to the western rim, 
and is finest on its western slope. 
Cornus pubescens and Thuja gigantea merely struggle up 
the Bitterroot river to the crossing, but are finely developed 
at the west base of the western rim with Acer glabrum, etc. 
Pinus monticola is very scarce on the eastern rim and 
Slope; it is a magnificent and abundant tree on the western, 
and finest near its summit. 
Frangula Purshiana, Pyrus fraxinifolia? and Abies 
grandis are found over the whole western rim, but are 
chiefly developed on its western slope and base. 
bies Menziesii is limited to its higher parts above 4000 
feet elevation. A. Williamsonii to vei above 4500 feet. 
Abies Mertensiana and Taxus brevifolia just straggle to 
its eastern slope, but are large and numerous on the western 
between 2000 and 4500 feet elevation. 
Finally, Crategus sanguinea and Cerasus mollis are con- 
fined to the lowest and warmest portions. 
Thus while nearly all are found on the western rim, and 

