GLACIAL DRIFT AND MARGINAL MORAINES. 93 



to the boundary and even upon the thhined waning margin of the ice, 

 so that any readvance may enclose the overwhehiied forest between 

 deposits of tilL Indeed, it appears probable that there were several 

 different stages of halt and readvance of the ice-sheet during its general 

 retreat from this area outside the moraines, and that the buried forest 

 surfaces do not belong wholly to one but to several fluctuations of the 

 ice-front. 



When the glacial melting had removed the comparatively thin outer 

 belt of the ice-sheet in the region of the upper Mississij^pi, its thicker 

 central portions, terminating with steeper gradients, flowed outward to 

 its chiefly restricted, limits with far more powerful currents than those 

 which had deposited the smooth expanse of the. early drift. This in- 

 creased vigor of the later ice action is shown by the almost universally 

 worn and striated surfaces of the underlying rock, by the accumulation 

 of large and continuous marginal moraines, and b}^ the irregular surface 

 of the drift inside the roughl}^ hilly morainic belts, with swells, ridges 

 and intervening hollows which hold many lakes and lakelets. 



Eleven retreatal moraines, marking stages of pause or slight forward 

 movement of the mostly retreating ice-margin, are determined in central 

 and northern Iowa and western Minnesota. The first or Altamont 

 moraine was accumulated when the extremity of the Minnesota and 

 Iowa ice-lobe reached to Des Moines ; when the second or Gary moraine 

 was formed, it terminated on the south at Mineral ridge, in Boone county, 

 Iowa ; at the time of the third or Antelope moraine, it had farther re- 

 treated to Forest City and Pilot mound in Hancock county, Iowa ; the 

 fourth or Kiester moraine was formed when the southern extremity of 

 the ice-lobe had receded across the south line of Minnesota and halted 

 a few miles from it in Freeborn and Faribault counties ; and the fifth or 

 Elysian moraine, crossing southern Le Sueur county, Minnesota, marks 

 the next halting-place of the ice in its recession northward. At the 

 time of formation of this fifth moraine the south end of the ice-lobe had 

 been melted back 180 miles from its farthest extent when the moraines 

 began to be amassed, and its southwest side had retired 80 to 50 miles 

 from the crest of the Coteau des Prairies in southwestern Minnesota 

 and the northeast part of South Dakota ; but while these great changes 

 in the area of the ice-lobe were taking place its eastern boundary for 30 

 miles southward from Saint Paul had fluctuated only slightly, so that a 

 broad compound morainic belt there represents the five moraines which 

 were formed on the south and west. Six later belts of marginal hilly 

 drift, named from localities of their typical development in Minnesota, 

 are in succession from south to north the Waconia, Dovre, Fergus Falls, 



