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TIIK "SLIDE ROCK" SITCKSSION. 



One feature \vliirh is noticeable in the topography alike 

 toward all points of the compass are the rock fields which com- 

 B extensive slopes of talus and are known as "rock slides 1 ' 

 or "slide-rock". Such areas consist of rock fragments mostly 

 under a foot in diameter. The succession of vegetation on these 

 areas is a matter of much interest and importance. As might 



. pected the rate of development varies much with the ex- 

 posure. 



One of these areas which faces the south in Hell gate Can- 

 yon a mile east of Missoula, offers considerable difficulty from 

 thi- standpoint of vegetation. This slope which rises at an angle 

 of about 40 degrees is one of the older slide rock areas since the 

 cliffs which formed it no longer are evident and the talus merges 

 smoothly into the urassy slope above. Viewed from a, distance 

 the shallow channels of occasional drainage are evident and these 

 have been preempted by Ribes cere um, Philadelphus Leirisii and 

 Amelanchier aini folia., which extend up and down the slope in 

 bushy, hedge-like rows. In about half a mile of this slope one 

 may count a score of Douglas spruce trees, old and misshapen. 

 A slightly greater number of yellow pines, and an equal num- 

 ber of smaller trees of each species, ten feet in height or less. 

 None of these occur above the line of the slide-rock. I'pon 

 closer inspection one finds old stumps of former large trees of 

 2'H) to 250 years of age. The larger living trees probably vary 

 from ".") to LM)0 years of age. There is immediate evidence that 

 on this area of approximately 80 acres there have been seed- 

 bejirinir trees for fully 200 years, yet the total stand of pine and 

 .as spruce combined numbers less than 100 trees, while the 

 number of young seedlings number a scant two score, the progeny 

 of about fifty s<-ed-l>eariiiL r trees. 



The fra-ments of the talus, at first -ra\ -. soon become spotted 

 with minute lichen 'jr-wth which finally covers the surface with 



'ini: almost Mack. \foarl of these lichens are close encrust- 

 niL' forms without ev.-n so much as a foliaceoiis margin of the 

 thalhis This rhan-je proceeds slowly, and much more slowly 

 on the southern than on the northern exposures. In the case 

 now under discussion . onsideral.le parts of the rock slope are 



