ISLANDS NEAR THE lOWAN MARGIN 119 



loess-like deposits of different age in some portions of the extra- marginal 

 territor3^ 



PAHA AND LOESS-KANSAN ISLANDS NEAR lOWAN MARGIN 



There are ridges and hills and other areas of considerable extent cov- 

 ered with loess inside the true lowan margin. Among the loess-covered 

 topographic forms occurring in this situation are the beautifully rounded 

 prominences called " paha " b}^ McGee. The paha are characteristic of 

 the marginal zone of the lowan, being limited to a space 5 or 10, rarely 

 20, miles wide, inside the extreme margin of the lowan drift. The paha 

 are covered with loess. They rise sometimes abruptly from the lowan 

 drift-jilain. An examination of their structure shows that the loess was 

 moulded over a core of rock or Kansan drift which stood prominently 

 above the general surface before the oncoming of the lowan ice. The 

 thin ice was divided by the prominence, flowed around it, and left it as 

 an island in the frozen sea, to receive, like true extra-marginal territor}^, 

 its mantle of loess. There is as yet no positive evidence that any lowan 

 drift was ever deposited over the summit of the prominent core of any 

 paha before the loess was laid down upon it. 



Besides the paha, there were in the marginal belt of the lowan area a 

 few anomalous highlands, embracing in one case at least as rnuch as fift}'' 

 square miles, that were surrounded but not overflowed by lowan ice. 

 Like other surfaces that were at the time free from ice, these were deeply 

 covered with loess. In these larger islands there are none of the char- 

 acteristics of the true lowan area. The loess rests on weathered Kansan 

 drift or on residual cherts and. clays. There is no lowan till, nor is there 

 a^ign of an lowan boulder. The topography conforms in all respects 

 to the type that distinguishes the extra-marginal area. The general 

 •aspect of the island-like plateaus rising above the lowan plain and sur- 

 rounded by lowan drift, as well as the structure and other characteristics 

 of the surface deposits, proclaim these as regions which had never been 

 invaded by lowan ice.* 



The unusual behavior of the lowan glacier, which expressed itself in 

 long, narrow, marginal lobes and isolated island-like spaces which the 

 ice surrounded but did not overflow, may possibly be accounted for by 

 conditions which seem, in some cases at least, to have attended the depo- 

 sition of the lowan loess. So far as this loess is of aqueous origin, the 

 phenomena lend support to the view that during the maximum advance 



* For a fuller account of some of these anomalous areas surrounded by lowan drift, yet retain- 

 ing all the characteristics of the extra-marginal territory, see the Report on Delaware county, 

 Iowa Geological Survey, vol. viii, p. 132. There is one similar area in Buchanan county. See same 

 volume, p. 210. 



