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Sierra Club Bulletin 



of other trees. Every tree so flooded dies, decays, and falls. 

 Thus, the so-called chance-falling of a few causes the fall of 

 many, which form a network, in the meshes of which the en- 

 tangled moisture is distributed with a considerable degree of 

 uniformity, causing the resulting bog to be evenly inclined, in- 

 stead of being cast into a succession of irregular terraces, one 

 for each damming log. 



Black flat meadow deposits, largely composed of humus, are 

 formed in lake basins that have reached the last stage of filling 

 up. The black vegetable matter is derived from rushes and 

 sedges decaying in shallow water for long periods. It is not 

 essential that these beds be constantly covered with water dur- 

 ing their deposition, but only that they be subject to frequent 

 inundations and remain sufficiently moist through the driest 

 seasons for the growth of sedges. They must, moreover, be 

 exempt from the action of overflowing flood-currents strong 

 enough to move gravel and sand. But no matter how advan- 

 tageous may be the situation of these humus beds, their edges 

 are incessantly encroached upon, making their final burial be- 

 neath drier mineral formations inevitable. This obliterating 

 action is going on at an accelerated rate on account of the in- 

 creasing quantity of transportable material rain-streams find in 

 their way. For thousands of years subsequent to the close of 

 the ice-winter, a large proportion of the Sierra presented a 

 bare, polished surface, and the streams that flowed over it came 

 down into the meadows about as empty-handed as if their 

 courses had lain over clean glass. But when at length the gla- 

 cial hard-finish was weathered ofif, disintegration went on 

 at a greatly accelerated speed, and every stream found all the 

 carrying work it could do. 



Bogs die also, in accordance with beautiful laws. Their 

 lower limit constantly rises as the range grows older. The 

 snow-line is not a more trustworthy exponent of climate than 

 the bog-line is of the age of the regions where it occurs, dating 

 from the end of the ice epoch. 



Besides bogs, meadows, and sandy flats, water constructs 

 soil-beds with washed pebbles, cobblestones, and large boulders. 

 The former class of beds are made deliberately by tranquil cur- 

 rents ; the latter by freshets, caused by the melting of the win- 



