84 IOWA ACADEMY OF SCIENCES. 



acid may be obtained, within six feet below the base of the 

 lower or Yarmouth soil. 



Between West Point and Denmark, a distance of seven miles, 

 records of thirteen wells have been obtained in which a soil was 

 found between the Illinoian and Kansan till sheets. The 

 thickness of the soil ranges from 2 to 5 feet and its depth below 

 the surface ranges from 16 feet to 45 feet; the usual distance to 

 the soil is about 30 feet. This represents, therefore, the com- 

 bined thickness of the lowan loess and Illinoian till sheet. 

 The loess, however, has a depth of but 5 to 10 feet. Of several 

 wells made at Denmark in 1894 to 1897 the writer has witnessed 

 the excavation, and finds that the leaching beneath the lower 

 soil extends about six feet into the Kansan till sheet. One of 

 the most satisfactory sections near Denmark is the following, 

 made on the farm of Mrs. Van Tuyl : 



FEET. 



Surface silt or loess of yellow color, slightly calcare- 

 ous and containing a few small pebbles near base . 7 

 Brownish yellow till, slightly calcareous and with 



few pebbles (Illinoian) 10 



Brownish yellow till very pebbly and calcareous 



(Illinoian) 8 



Blue clay with few pebbles (Illinoian) 10 



Black mucky soil with wood (Yarmouth) 2 



Brownish-yellow till (Kansan) 12 



Hard blue till (Kansan) 6 



Limestone 4 



Total 59 



In this connection it may be remarked that several of the 

 wells in the vicinity of Denmark pass through 25 or 30 feet of 

 oxidized Kansan till and enter rock without striking a blue till, 

 but exposures in ravines both north and south of the village 

 show a dark blue-black till thickly set with fragments of wood. 

 This occurs at a level lower than the rock surface at Denmark 

 and has a striking similarity to exposures in other parts of the 

 state, which are suspected to be pre-Kansan in age. 



EXPOSURES AT DAVENPORT, IOWA. 



The Illinoian till sheet as above nolied is known to overlap 

 the Kansan as far north as Davenport, Iowa. There are excel- 

 lent exposures of both sheets within the limits of that city and 

 also at points a few miles west, near Blue Grass. An exposure 

 in Davenport, on Eighth street, between Myrtle and Vine, was 



