6 



Sierra Club Bulletin. 



What, however, impelled the rocks and the tree 

 stump downward? None of them appeared in motion, 

 and none when dislodged, would slip or roll. The 

 slope was not steep enough for that. Observation 

 further showed that no stripes ever occur on very- 

 steep slopes — they are restricted to surfaces of moder- 

 ate inclination such as the crowning portions of the 

 domes, and wherever the declivity approaches the 

 "angle of repose" the stripes invariably come to an 

 end. A pretty and striking instance was seen on a 

 small domed spur in the Little Yosemite Valley. 

 Here the stripes, diverging downward like meridians 

 on a globe, all terminated abruptly as by concert at 

 the same level, the same parallel of latitude. Below 

 that line, evidently, the debris had slid or rolled away. 

 The inclination here, it should be noted, was too great 

 to stand on safely, but farther up, among the stripes, 

 one could walk even with hobnails by exercising a 

 little care. 



It is to be inferred from the above that a slow 

 -motion of the debris is essential for the production of 

 the stripes. The explanation is here offered that the 

 debris is urged down little by little by snow and run- 

 ning water and even the rockgrains washing from above, 

 in fact by all agents co-operating with gravity to over- 

 come the frictional resistance of the floor. Most 

 potent, no doubt, are the heavy snows of winter, and 

 there is good reason to believe that the greatest prog- 

 ress is made under their influence. For, on inclined 

 surfaces of this sort, snow does not lie wholly inert, 

 but almost imperceptibly creeps downward — the same 

 as it does on the roofs of barns and sheds. As the 

 entire layer advances, it naturally tends to drag the 

 debris with it. 



The total progress thus effected may not exceed an 

 inch or two per year, and this estimate, if it is at all 

 correct, lends additional significance to the stripes : 

 they indicate not merely the route traveled over by 



