53G STEVENSON— FORMATION OF COAL BEDS. [November 3, 



discharf^e was thirty-eight times as great as that during the abnor- 

 mall}- wet sinunier of 1889; five hunch-ed and seventv-nine times that 

 of the average low water discharge ; it closely approximated that of 

 the Mississippi in ordinary years and was two fifths of the discharge 

 by that river during the flood of 1858. At Great Falls, the torrent 

 was OIK' third of a mile wide and 150 feet deep. This was a flood 

 of unprecedented extent, such as might not be repeated in centuries. 

 It should afford full opportunity for determining the ability of floods 

 to remove vegetation. As McGee entered into no detail in his admin- 

 istrative report, the request was made that he would give such infor- 

 mation as seemed proper. His letter" is in complete detail and the 

 following citations are taken from it. 



" Tlie most impressive river flood I ever saw occurreLl in the Potomac 

 several years ago, wlien during June a series of rains occurred in such 

 order about llie headwaters as to raise the river far above any high stage 

 previously recorded — indeed I inferred from its effect in l)ending smaller 

 trees in connection with the undisturbed attitude of the older trees that it 

 far exceeded any flood of the preceding 150 years. Tlie discharge was not 

 accurately measured, because the flow was too swift to get a weight into 

 tile water, -1)ut approximate measurements gave a discharge comparable with 

 that of the Mississippi at ordinary stages. After tiie water sulisided I went 

 over the flooded ground with care; and tliis is what I found — the bottom 

 being irregular, chiefly wooded, partly in field and pasture; in the woods, 

 frees of less than, say, a foot and a half in cHameter, were bent down stream 

 and largely robbed of foliage, and a few were broken off, leaving snags; 

 the higher trees had generally lost branches and most of their foliage (the 

 water having risen forty to sixty feet, or well toward the tops of the highest 

 trees) ; here and there, esiiecially near llie chamiel, a tree or clump of trees 

 had been uprooted and swept away, thougli not more than say one or two 

 per cent, of the wood in tree or branch was gone. Here and there in the 

 woods, where tlie current was concentrated by rocks or large trees, a gully, 

 generally two or three feet deep, as ni;in\- yards wide and as many rods 

 long, had been cut out; elsewhere, especially where rocks and trees had 

 slackened the local current, tliere were bars and banks of sand ; and gen- 

 erally throughout the w'oods there was a layer of silt, of course, left chiefly 

 by the subsiding waters overspreading the soil — which usually was unmodified 

 otherwise. From a little field, in-eviously on the l)ottom, a short distance 

 above Georgetown, the entire crop and the soil to ])low-depth or more was 

 removed; and in a sloping and somewhat rocky tract of pasture land, up- 

 stream from the field, the sward was irregularly furrowed by gullies 

 ordinarily a few feet deep and as many yards wide — the number being such 



'*0f December 6, igio. 



134 



