DRAINAGE OF THE GLACIAL PERIOD. 321 



ing at the rate of three miles an hour, to carry off this surplus 

 drainage of 500 cubic miles accumulating each summer. 



If it should be supposed that the current would be much 

 faster than three miles an hour, it is proper to note that 

 from the known facts about the northerly depression of the 

 land during the latter part of the glacial period it is extremely 

 probable that the gradient of the stream was very much 

 less during the time of these floods than it is now. Further- 

 more, the gradient of the stream was much diminished by the 

 flooded condition of the Mississippi into which the Missouri 

 enters. For, the glacial floods pouring into the Mississippi 

 and Ohio were of such enormous magnitude as probably to 

 raise the level of the Mississippi 100 feet or more, during these 

 summers. It is not at all unreasonable, therefore, to expect 

 to find indications of glacial floods in the Lower Missouri 

 rising to a height of 200 feet or more. 



And these we do find. In 1902, Dr. Ball of the Missouri 

 Geological Survey found a number of large Canadian bowlders 

 in the valley of the Osage River sixty miles above its junction 

 with the Missouri and forty miles south of the extreme limit 

 of the extension of glacial ice. There is no way to account for 

 such bowlders in that position except on the supposition 

 that they were floated in there by a backward current from 

 the Missouri when its glacial floods, bearing floating masses of 

 ice with Canadian bowlders upon their surface, reached a 

 height of 200 feet. Since there was no melting ice in the valley 

 of the Osage to increase its volume, such an eddy in the cur- 

 rent would be sure to set up that valley and supply the cause 

 necessary to explain what was a very puzzling problem when 

 first propounded. Such floods also are needed in the Missouri 

 Valley to account for the many level-topped extensive accu- 

 mulations of loess (a fine river loam to be described more in 

 detail in a later chapter) which occur at numerous points 

 throughout the valley. 



