Studies in the Sierra 



71 



rows, are twenty or thirty yards apart. After belt number i 

 was laid down, the glacier evidently withdrew at a faster rate, 

 until a change of climate as regards heat or cold, or the occur- 

 rence of a cluster of snov/ier years, checked its backward mo- 

 tion sufficiently to afford it time to deposit belt number 2, and 

 so on; the speed of the dying glacier's retreat being increased 

 and diminished in rhythmic alternations of frost and thaw, 

 sunshine and snow, all of which found beautiful and enduring 

 expression in its ridged moraines. The promontories P P are 

 portions of a terminal soil-belt, part of which is covered by the 

 lake. 



Similar fields of corrugated moraine matter occur farther 

 down, marking lingering and fluctuating periods in the reces- 

 sion of the glacier similar to the series we have been studying. 

 Now, it is evident that if, instead of thus dying a lingering 

 death, the glacier had melted suddenly while it extended into 

 the Mono plain, these wide soil-fields could not have been made. 

 Neither could the grand soil-belt of the western flank have ex- 

 isted if the ice-sheet had melted in one immense thaw while it 

 extended as a seamless mantle over all the western flank. For- 

 tunately for Sierra vegetation and the life dependent upon it, 

 this was not the case; instead of disappearing suddenly, like a 

 sun-stricken cloud, it withdrew from the base of the great soil- 

 belt upward, in that magnificently deliberate way so character- 

 istic of nature — adding belt to belt in beautiful order over lofty 

 plateaus and rolhng hills and valleys, wherever soil could be 

 made to lie. 



Winds and rains, acting throughout the ample centuries, 

 smooth rough glacial soils like harrows and rollers. But this 

 culture is carried on at an infinitely slow rate, as we measure 

 time. Comparing the several moraine-fields of Bloody Cafion, 

 we observe that the ridged concentric structure (Fig. i) be- 

 comes gradually less distinct the farther we proceed out into 

 the plain, just as the plow-ridges in a farmer's field become less 

 distinct the more they are harrowed. Now, the difference in time 

 between the deposition of contiguous moraine-fields in Bloody 

 Canon is probably thousands of years, yet the difference as re- 

 gards smoothness and freshness of aspect corresponding to this 

 difference in time is in some instances scarcely discernible. In 



