5«4 



SAMUEL CALVIN 



and disposed in numerous sheets and ridges, were laid down 

 throughout northeastern Iowa, on top of the Kansan till, over the 

 area which, but a short time previously, had been abandoned by 

 the retreating ice. They are true outwash gravels. Exposure 

 during the long interval between the Kansan and the Iowan has 

 wrought profound changes in the decomposable granites and other 



Fig. i. — View in the old gravel pit near Doris, Buchanan County, Iowa, showing 

 Buchanan gravels, a deposit contemporaneous with the closing phase of the Kansan, 

 overlain by the younger Iowan drift. 



constituents of the Buchanan deposits; and now these gravel 

 deposits become unimpeachable witnesses to the fact that glaciers 

 belonging to a stage long subsequent to the Kansan distributed a 

 new sheet of till differing from the Kansan in composition, color, 

 and petrological contents. The Iowan is yellow; the Kansan, 

 while normally blue, sometimes weathers yellow; where yellow 

 Iowan rests directly on yellow weathered Kansan, the line of 

 contact may not be as distinct and satisfactory as some observers 



