THE "slide rock" SUCCESSION 115 



still as bare as when first formed. Elsewhere, however, espe- 

 cially on more favored exposures the slide-rock has become cov- 

 ered with dark lichens and has at a distance the appearance of 

 coal. 



"Where a trace of soil comes into the talus, wind blown or 

 washed, it supports the following plants : 

 Afiropijrcm spicatum Balsamorrhiza sagiitata 



ClarJcia pulcJiella Delphinium iicolor 



Leptotaema multifida Achillea lanulosa 



Pentstemon Wilcoxii Woodsia scopiilina 



Artemisia frigida 



The forests of the northern and eastern slopes are subject 

 to an entirely different set of conditions. Long after the snow 

 is gone from the southern and western exposures it lies in deep 

 drifts on the opposite slopes. Instead of an almost vertical sun 

 as on the former the latter exposure may receive very little 

 direct illumination. It is sheltered from the prevailing winds. 

 As a result of these conditions, the ground water is fairly plen- 

 tiful and lasts later into the season. These conditions are usually 

 favorable in many places for a near-mesophytic vegetation in 

 contrast to the xerophytic on the opposing slope. 



As typical of conditions over a large part of western Mon- 

 tana, the principal discussion will deal with the south wall of 

 Hellgate Canyon just opposite and distant about a quarter of a 

 mile from the slope described above. This slope, of about 

 the same angle, has several outstanding crags, and rugged ridges 

 extending up and down the north slope. Between these ridges 

 are depressions occupied to a large extent by steep and extensive 

 areas of unstable talus. 



The forest of the north slope is mainly Douglas spruce and 

 western larch. Yellow pine does not amount to so much as one 

 hundredth part of the stand, and is found chiefly on the tops 

 of the ridges and at higher elevations where it approaches the 

 crest of the ridge toward the southern exposure. This undoubt- 

 edly is due to its demand for light. In a few places on the 

 higher slope are thickets of lodgepole (Finns contorta) and here 

 and there a Rocky Mountain juniper (J. scopulorum) . 



The tops of the ridges extending up and down the slope are 

 occupied by the oldest and largest trees, chiefly Douglas spruce 



