.M"GEE — XOTES 0\ THE GEOI.OGV OF MACOX CO., MO. 315 



continuous sheets several feet in length ; and pebbles and bowl- 

 ders are frequently incrusted and cemented by the calcareous 

 sheets or attached to the nodules. Sand is an unimportant and 

 inconspicuous element in the drift of Macon county. 



Although the drift sometimes appears to be vertically homoge- 

 neous in exposures however deep, the better sections exhibit cer- 

 tain constant differences between its basU and summital portions : 

 the upper third or half is more or less regularly bedded horizon- 

 tally, contains fewer and smaller and more irregularly dissemin- 

 ated pebbles than the lower, and exhibits more abundant calcare- 

 ous concretions and sheets ; while the lower portion is generally 

 massive and destitute of regular bedding, and, in short, exhibits 

 throughout the minute but readily recognizable structural and 

 other features which characteri-ze the glacial drift of the upper 

 Mississippi valley generally. The distinction is indeed so 

 strongly marked as to be coinmonly recognized by the miner and 

 well-digger; yet the two phases invariably intergraduate imper- 

 ceptibly. 



The structural difference between the inferior and superior por- 

 tions of the otherwise indivisible drift-sheet is evidently genetic : 

 the abundant and well striated local and sub-local bowlders and 

 the characteristic structure and texture of the deposit, the plan- 

 ing of the rock surface (indicated by configuration rather than 

 striation, so far as observed), and the displacement of ledges, all 

 prove that the lower portion of the deposit is the homologue of the 

 till, or unmodified glacial drift, of Iowa, Wisconsin, northern Illi- 

 nois, and the upper Mississippi valley generally ; while the strati- 

 fication, the assortment of pebbles and other materials, the /oess- 

 kiiidchen and other structural characters, and the remarkable 

 horizontality of both bedding and surface-lines over a great area, 

 all indicate strongly that the upper portion is water-laid. 



The superior division gives origin to soil and sub-soil of pecu- 

 liar tenacity and intractability, evidently by reason of the finely 

 comminuted coiditionof its materials and the presence of a small 

 percentage of unoxidized rock debris, and the consequent tend- 

 ency to pack closely and undergo partial cementation. Unless 

 carefully and judiciously tilled, the soil is prone to *Mrown" 

 in spring and "bake" in summer, especially on the imperfectly 

 drained plains forming the uplands ; but these characteristics are 



