5G2 STEVENSON— FORMATION OF COAL BEDS. [November 3. 



floods are checked as surely as though dammed by a mountam. 

 Logjams are not swept out by the greatest floods, though the accu- 

 mulation is merely superficial ; in spite of floods, they accumulate at 

 the upper end while decaying at the lower. If floating debris enter 

 a lake of moderate size, it finds its way directly to the outlet ; but if 

 the lake be large and disturbed by waves, the debris is scattered 

 along the shores. Finely divided organic matter carried out by 

 floods is in minute quantity compared with the mineral matter and 

 it is deposited along with the fine mud. 



4. The trees as well as the humus swept out by floods were not 

 uprooted by the running water. Their presence in the current is 

 due to the undermining of banks composed of unconsolidated mate- 

 rial, so that trees, humus and the rest fall together into the water to 

 be carried away. The damage thus done is very small — the drift 

 carried by the lower Mississippi being the accumulation from the 

 soft banks of more than 20,000 miles of river, the length of tor- 

 rential and semi-torrential streams being neglected, as they contribute 

 an insignificant proportion of the mass. The quantity of driftwood 

 in all is unimportant, when one considers the area into which it is 

 swept. Comparatively little lodges on its way down the larger 

 streams and most of that is buried in muds as " towheads " or 

 " snags " or accumulates in rafts to disappear by rotting. A small 

 part is stranded on deltas, far less than has been supposed, for in 

 the Mississippi delta the deposits, supposed to be of driftwood, are 

 now known to be old swamps and forests buried in situ, ^tuch 

 finds its way to shores more or less distant where, after having been 

 for long time the plaything of winds and currents, it is cast in bat- 

 tered condition, scattered here in clumps or in individual pieces to 

 decay or to be buried in sands. But the greatest part floats until, in 

 half-rotted condition, after long exposure, it finds its way to the 

 depths of the sea, to litter the bottom in areas, 1,000 to 1,500 fathoms 

 below the surface, where, mingled with remains of marine animals, 

 it will become part of bituminous shales, with here and there a pot 

 of impure coal. 



5. The conception that moving water, under any known or re- 

 corded conditions, can uproot forests and sweep oft' peat bogs from 



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