Studies in the Sierra 



8i 



do. Upon the clay-beds thus created avalanches frequently 

 pile tangled masses of tree-trunks, mingled with burs and 

 leaves and rocky detritus scraped from the mountain side. 

 Other layers of mud are deposited in turn, together with fresh- 

 et-washings of sand and gravel. This goes on for centuries 

 from season to season, until at length the basin is filled and 

 gradually becomes drier. At first, the soil is fit only for sedges 

 and willows, then for grasses and pine-trees. This, with minor 

 local modifications, is the mode of creation of the so-called flat 

 and meadow soil so abundantly distributed over all parts of the 

 range. 



Genuine bogs in this period of Sierra history occur only in 

 shallow alpine basins, where the climate is sufficiently cool for 

 the growth of sphagnum, and where the surrounding topo- 

 graphical conditions are such that they are safe, even in the 

 most copious rains and thaws, from the action of flood-cur- 

 rents capable of carrying stones and sand, but where the water 

 supply is nevertheless sufficiently constant and abundant for 

 the growth of sphagnum and a few other plants equally fond 

 of cold water. These dying from year to year — ever dying 

 beneath and living above — gradually give rise to those rich 

 spongy peat-soils that are the grateful abodes of so many of the 

 most dehghtful of alpine plants. 



Beds of sloping bog-soil, that seem to hang like ribbons on 

 cool mountain sides, are originated by the fall of trees in the 

 paths of small creeks and rills, in the same climates with level 

 bogs. The interlaced trunks and branches obstruct the feeble 

 streams and dissipate them into oozing webs and stagnant 

 pools. Sphagnum speedily discovers and takes possession of 

 them, absorbing every pool and driblet into its spongy stems, 

 and at length covers the muddy ground and every log and 

 branch with its rich rounded bosses. 



Here the attentive observer is sure to ask the question. Are 

 the fallen trees more abundant in bogs than elsewhere in the 

 surrounding forest? — and if so, then, why? We do find the 

 fallen trees in far greater abundance in sloping bogs, and the 

 cause is clearly explained by young illustrative bogs in process 

 of formation. In the first place, a few chance trees decay and 

 fall in such a manner as to dam the stream and flood the roots 



