538 STEVENSON— FOR.MATIOX OF COAL BEDS. [November 3. 



and the drifted material is raised above the high level; but rings of 

 silt left on trees, all on approximately the same level, show the true 

 waterline. In this way he determined the extent of the flood. The 

 houses, made of lumber, were lifted from their foundation and were 

 dashed to pieces against rocks or trees. 



Wilkes^" made use of the same method. In speaking of floods 

 on the Willamette river of Oregon, he says that the sudden rises of 

 the stream are remarkable, the perpendicular height of the flood 

 being at times as much as 30 feet, the limit being marked very dis- 

 tinctly on trees along the banks. In New South Wales " near the 

 source of streams, grass is to be seen attached to the trunks of trees 

 thirty feet above the present level of the water, which must have 

 been lodged there by very great- floods." This is a commonplace 

 condition ; the writer observed it at the head of Sacramento bay in 

 California almost forty-five years ago. He saw many bunches of 

 drift stufif entangled in branches of trees at 10 to 15 feet above the 

 water level, and he was astonished by the fact that so great a flood 

 had done no injur}- even to the shrubs growing among the trees. 



Rk'crs in Great Interior Basins. — Excellent descriptions of floods 

 within the Mississippi-Missouri area are given in reports of the 

 Ignited States Weather Bureau, tliose by Morrill and FrankenfielcF' 

 being the most comprehensive. 



Man's skill has brought about great changes in the lowlands of 

 the Mississippi. The fertilit}' of that region from the mouth of the 

 Ohio to the Gulf of Mexico early led to settlements at many places. 

 But the periodic floods of the river rendered agricultural operations 

 precarious and levees were constructed for protection. Eventually the 

 construction of such levees was assumed by the Federal government 

 and they now protect a vast area from overflow. The region, now 

 exposed to devastation under ordinary circumstances, is very small, 

 but, during abnormal floods, the levees sometimes give way and 



'" C. Wilkes, " Narrative of the United States Exploring Expedition," 

 1845. Vol. IV., p. 358; II.. p. 269. 



" P. Morrill, " Floods of the Mississippi River." Rep. Chief of Weather 

 Bureau for 1896-7, Washington, 1897, pp. 371-431. H. C. Frankenfield, "The 

 Floods of the Spring of 1903 in the Mississippi Watershed," Weather 

 Bureau l>ull., 1904. 



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