Studies in the Sierra 



77 



available, and the trees that venture upon them are in constant 

 danger of their lives. These unplanted beds occur most com- 

 monly at the base of clififs intersected by feldspathic veins, the 

 decomposition of which causes the downfall of additional mate- 

 rial from year to year. On the contrary, the rougher and far 

 more important soil-beds resulting from earthquake avalanches 

 are formed almost instantaneously, without being subsequently 

 augmented in any appreciable degree for centuries. The trees, 

 therefore, and various shrubs and flowers which find them tol- 

 erable or congenial dwelling-places soon take possession of 

 them, and soothe their rugged features with a mantle of waving 

 verdure. 



At first thought no one would suppose that in a tumultuous 

 pellmell down-crash of rifted rocks any speciahzation could be 

 accomplished in their deposition. Both the suddenness and the 

 violence of the action would seem to preclude the possibility of 

 the formation of any deposit more orderly than a battered rub- 

 bish-heap. Every atom, however, whether of the slow glacier 

 or swift avalanche, is inspired and directed by law. The larger 

 blocks, because they are heavier in proportion to the amount of 

 surface they present to the impeding air, bound out farther; 

 and, because obstructions of surface irregularities have less 

 efifect upon larger blocks, they also roll farther on the bottom 

 of the valley. The small granules and sand-grains slip and roll 

 close to the cliff, and come 

 to rest on the top of the ta- 

 lus, while the main mass of 

 the talus is perfectly gradu- 

 ated between these extremes. 

 Besides this graduation ac- 

 complished in a vertical and 

 forward direction, beautiful 

 sections are frequently made 

 in a horizontal and lateral 

 direction, as illustrated in 

 Figure 4. A B is a kind of 

 natural trough or spout near 

 the base of the cliff, directed 

 obliquely downward, into 



