8 



Sierra Club Bulletin. 



ation of the gradient, or perhaps through the pressure 

 of an exceptionally heavy snow fall. 



To come back now to the floor of the Little Yosemite 

 Valley equipped with this insight into the stripe-pro- 

 ducing process, let us look it over somewhat more 

 closely. The feature that strikes us as most puzzling 

 is the total absence of debris of any kind. Whatever 

 material once traveled over the floor has in some man- 

 ner disappeared. But not wholly, for here, near the 

 east edge of the tract, lies a boulder weighing some 

 twelve or fifteen pounds (see Fig. 3) at the end of a 

 long and glorious stripe. More than twenty feet it 

 stretches, gradually fading in the distance like the 

 smoke trail of a locomotive. A finer example would 

 be difficult to find. The upward dimming of the stripe 

 is in itself significant: so excessively slow has the 

 progress of the boulder been that the lichens are already 

 beginning to encroach again on the upper end, slow- 

 growing plants though they be. When it is considered 

 that rocks uncovered by road grading a score of years 

 ago show scarcely any new lichens to-day, the great 

 span of time represented by this stripe becomes doubly 

 impressive. Its upper end, indeed, may date back to 

 the time the Yosemite Valley was discovered. 



But this stripe, after all, diflPers somew^hat from the 

 others on the floor. The rank and file are shorter and 

 narrower; many split or fork irregularly, and all have 

 ceased to grow in length through the removal of the 

 debris that made them. Yet that material did not 

 roll away, for the floor maintains about the same grade 

 throughout and many stripes begin in the same lati- 

 tude where others end. How, then, are these traits to 

 be interpreted? 



In the first place it seems certain that the material 

 in question consisted of small, light fragments that 

 were easily disturbed and thrown from their path by 

 the feet of passing men or animals. That this must 

 have happened more than once seems likely in view of 



