368 NATURAL HISTORY BULLETIN. 



posits above and including the Kansan drift: 1.) Kansan drift; 

 2.) Kansan residual sands and gravels (Buchanan); 3.) Gum- 

 bo; 4.) Black soil (Yarmouth); 5.) Post-Kansan loess; 6.) Illi- 

 noisan drift; 7.) Illinoisan residual sands and gravels; 8.) Black 

 soil (Sangamon); 9.) Post-Illinoisan loess; 10.) Iowan drift; 

 11.) Iowan residual sands and gravels ( Peorian); 12.) Black 

 soil; 13.) Post-Iowan loess; 14.) Wisconsin drift; 15.) Wis- 

 consin residual sands and gravels; 16.) Post-Wisconsin loess. 

 The post-Kansan loess is widely distributed, very compact, of 

 a pale bluish gray color, with numerous iron-tubules and some 

 lime nodules, and it is frequently fossiliferous, the fossils being 

 uniformly very fragile ("rotten"), and closely imbedded so that 

 it is often difficult to remove them entire. 



The post-Illinoisan loess is restricted to the southeastern 

 part of the state, and is not as prominent as the following. 



The post-Iowan loess is yellow or brownish, partially leached 

 only in its lower part in thick deposits, often fossiliferous, the 

 fossils usually being well-preserved and firm, and it is best 

 developed near the Iowan drift margin. 



The post-Wisconsin loess is not a conspicuous member of 

 the series, appearing in patches, and as a thin veneer, in the 

 northern and northwestern parts of the state. 



These several loesses are quite distinct near the drift bor- 

 ders, but the distinction grows less clear as we recede from 

 the drift-margins, especially southward, and finally practically 

 disappears, probably in the regions in which plant -life was 

 not wholly destroyed by the advances of the several ice - sheets 

 succeeding the Kansan. 



Manifestly, however, there were several periods of loess for- 

 mation, and they appear to have been interglacial and post- 

 glacial. Far beyond the border of the newer drift sheets, 

 however, the sharp lines of distinction between them disap- 

 pear, and there the deposits of loess probably represent the 

 combined accumulation of several interglacial and later drift 

 periods. 



