Semi-Centennial Volume. 117 



Aftonian beds of western Iowa, and were thought at first to be a river 

 deposit like them, but further study has shown them to be uniformly 

 fine and evenly stratified. 



Similar beds have been found south of the creek which enters the 

 Missouri south of the union depot, in the river bluffs and at frequent 

 intervals for three or four miles southwest. A fine exposure occurs half 

 a mile southwest of Forest park, on the north of the creek, where a cliif 

 of slightly consolidated sand stands fifty feet high, which is capped with 

 ten feet of till, the lower part of which is banded as though laid in water. 



It appears, therefore, that the deposit was not the direct work of the 

 Missouri, for it lies in the valley of a tributary rather than of that 

 stream itself. 



The most rational interpretation yet suggested is the following: 



The chert graves mark the level of pre-glacial drainage. This at 

 Atchison is at least twenty-five or thirty feet lower than the corre- 

 sponding level in the Kansas river valley near Linwood, which indicates 

 that Atchison was in the valley of a different master stream, presumably 

 one which was a predecessor of the Platte of Nebraska, and of the Grand 

 river, Missouri. Traces of its trough seem to have been found near 

 Conception and Stanbury, Mo. 



The advance of the Kansan ice sheet from Des Moines river valley 

 southwest dammed the Platte-Grand river near Stanbury, causing a 

 temporary lake or lakes in the valleys of that and of its tributaries, in- 

 cluding that at Atchison. The water rose till it flowed over the divide 

 south into the Kansas valley, presumably along the line of the present 

 Missouri there. 



This seems corroborated by the occurrence of a cobble and boulder 

 deposit at Weston, Mo., and south, about 140 feet above the present 

 Missouri. This, when discovered over twenty years ago, was thought to 

 indicate rapids, very like such as this explanation would imply. 



In frankness it should be acknowledged that similar lacustrine beds 

 have not yet been found along the Nemaha, Nebraska, and Wolf creek, 

 Kansas, as we should expect. Perhaps another twenty years may clear 

 up the discrepancy. 

 March 23, 1918. 



