748 T. C. CHAM BERLIN 



glacio-fluvial deposits during the ice age. The great examples 

 are the larger members of the upper Mississippian system, and 

 pre-eminent among these, the Missouri river whose bottom deposit 

 is mainly sand and silt of an unusually mobile type. The vain 

 struggle of the United States engineers to restrain the destructive 

 shiftings of this river within bounds amenable to navigation and 

 to permanent improvement on its banks, has brought out data 

 which amply illustrate this profound instability, but this can only 

 be fully appreciated by a detailed study of the reports of the 

 chief of engineers. 1 Mr. L. E. Cooley, in his report for 1879, 

 (p. 1066), makes the following among many other pertinent 

 statements : 



"To understand the difficult nature of the problem presented 

 here [Eastport bend, on the Missouri river much above Lans- 

 ing, but where the conditions are not essentially different J, it is 

 necessary to consider that at high-water, the banks are under 

 water to a depth of three or four feet, and the current velocity 

 is as great as seven or eight miles an hour. The erosion of the 

 banks for several years past has been at the rate of about 1,100 

 feet per annum. When this was stopped bv our revetment, a 

 tremendous scour was set up, carrying the bed of the river thirty 

 or forty feet below its normal position ; in fact, the scour 

 undoubtedly extended to the solid rock underlying the valley." 

 And again [loc. cit., p. 1071), "In many of the borings which 

 have been made here, indurated clay balls with vegetable matter 

 covered with a coating of sand, along with a motley collection 

 of gravel stones, are found within a short distance of permanent 

 strata. A precisely similar collection containing gumbo balls in 

 a soft state was dredged from sixty feet depth at the works. 

 These balls are from cutting banks, and the proof is conclusive 

 that since the river has been running in silt banks as at present, 

 scour has occasionally, at least, reached permanent strata at 

 seventy to ninety feet depth." 



Mr. Concannon informed me that eleven years ago the 



1 Professor Todd has called attention to some of these remarkable facts in his 

 bulletin on the " Moraines of Southeastern Dakota and their Attendant Deposits," 

 Bull. U. S. GeoL Survey, No. 158, pp. 150, 151. 



