Little Studies in the Yosemite Valley. 



9 



the side of the cut. CHmbing out of the road, one may follow 

 the curving crest for a few hundred feet until it becomes lost 

 in the coarse debris at the base of the Cathedral Rocks. 



North of the river, the ridge runs west of the road, stretching 

 across the valley for half a mile like a steep-sided, narrow- 

 crested embankment. At first fully fifteen feet high, it grad- 

 ually loses in height and prominence, and finally, toward the 

 road forks, appears to die out altogether. However, it does not 

 end here, but merely becomes buried under the toe of the huge 

 debris slopes descending from the cliffs about Ribbon Falls. 



Were this pecuHar ridge, unique in the configuration of the 

 valley floor, situated in the open so that its form stood out 

 conspicuously above the surrounding flat, no doubt from the 

 first it would have attracted attention; its signifixance would 

 have been looked into and now would be common knowledge. 

 As it is, dense thickets of pine and cedar effectually mask the 

 ridge ; most passers-by are not aware of its existence, and even 

 some of the scientists who have studied the valley in detail have 

 missed the feature and thereby the key to the recent geological 

 history of the entire valley floor. 



The boulder ridge in question is a typical glacial moraine; 

 no experienced glacialist would for a moment hesitate in identi- 

 fying it as such. It is a terminal moraine, properly speaking, — 

 that is, a debris ridge of the sort which glaciers commonly build 

 up at their fronts. All glaciers, as is well known, carry a con- 

 siderable amount of rock debris derived from the floor and 

 sides of the valleys through which they advance, and this 

 material, as the ice melts away, is released at the lower end. 

 While the front of a glacier is inherently subject to frequent 

 oscillations, some years melting back, at other times advancing, 

 there are nevertheless occasional periods of relative constancy 

 during which the front remains stationary, or very nearly so. 

 It is then that this ice-freed debris accumulates in the form of 

 an embankment or morainic ridge, as it is technically termed. 

 When, moreover, the period of quiescence follows immediately 

 upon one of advance and pronounced erosional activity, during 

 which the glacier heavily loaded itself with debris, the moraine 

 is likely to assume proportions that will enable it to endure as 

 a topographic feature of some permanence. 



