Studying the Yosemite Problem 



141 



A long and laborious task this mapping of moraines proved 

 to be. For the ice of each period advanced and retreated 

 not in simple, uninterrupted cycles, but with many minor 

 fluctuations. After the glaciers had reached their maximum 

 extent and began to recede, they made repeated feeble re- 

 advances, pulsations, as it were, of progressively diminishing 

 strength, each of which left a cordon of moraines to witness 

 its magnitude. As a consequence there are now several series 

 of moraines, both across the valley floors and along the moun- 

 tain slopes. The former, or terminal moraines, record the 

 oscillations of the glacier ends, while the latter, or lat*^ral 

 moraines, mark the width of the ice streams and their level 

 at each stage. 



The actual mapping of the moraines was accomplished 

 throughout by pacing surveys along their crests, directions 

 being taken by hand compass and altitudes by aneroid. Sel- 

 dom was it practicable to sketch the moraines from an elevated 

 vantage point, for, composed as they are of disintegrating 

 rock debris, moraines inherently offer good ground for vege- 

 tation and are almost everywhere ensconced in forest or in 

 chaparral. This fact itself, as one may imagine, contributed 

 not a little to the slowness of the mapper's task. The daily 

 routine consisted of tramping through the woods or fighting 

 through the brush, always counting paces — for the distances 

 must be faithfully measured, no matter how bad the going, 

 in order that the moraine crests might be correctly plotted on 

 the map. Several months were devoted to this work, it being 

 stopped only by the advent of the snow early in December. 



The results obtained were, to say the least gratifying. As 

 the moraine map grew it began to tell a story — a story sur- 

 prisingly vivid and complete in details, considering the elusive 

 character of the facts with which it dealt; a story, too, that 

 rather insis<-ed on shaping itself and occasionally took turns 

 unexpected by the investigator. Indeed the writer will frankly 

 confess that the glacial history of the Yosemite country 

 turned out in many respects different from what he had an- 

 ticipated, — different, too, from the various interpretations 

 given by those who have vfitten about the ancient Sierra 

 glaciers. Early in the investigation the moraine map 



