IOWA ACADEMY OF SCIENCES. 93 



of cases to give the primary suggestion of the solution of the 

 difficulty, leading one to seek for and find other and surer evi- 

 dence. 



THE AFTON-THAYER EXPOSURES. 



The Aftonian beds are not positively known to occur in or 

 immediately adjacent to the city of Afton; the latter is, how- 

 ever, the best known town near the original exposures. The 

 beds are seen well exposed at three abandoned gravel pits 

 located three to six miles east of Afton proper. These are (1) 

 between Afton Junction and Talmage; (2) about one mile 

 southeast of the Junction on the south side of Grand river; 

 (3) about three-quarters of a mile west of Thayer on the south 

 side of the Chicago, Burlington & Quincy railway. For con- 

 venience these will be called the Afton Junction, Grand River, 

 and Thayer pits, respectively. The Afton Junction pit shows 

 the overlying loess, the Kansan drift and the gravels with cer- 

 tain buried silts or loess beds below the latter. The Grand 

 River exposure shows the upper and lower drifts with the 

 gravels between. The Thayer exposure shows the gravels and 

 the overlying drift with certain sands and fine clays between. 



Afton Junction. — The pits at this place are about 1,500 feet 

 north of the railway station, on the west side of the Chicago 

 Great Western. They have been opened along the sides of a 

 small stream running east and emptying into Grand river. 

 The north side of' the pit is bilobate, the minor lobe being to 

 the east and not directly in line with the main face of the pit. 

 The two lobes in fact form an arc of a rude circle rather than a 

 straight face. Between the two lobes is a small ravine which 

 has cut down to, but not through, the gravels. The main face 

 (Plate v)'is about 1,000 feet long and has a maximum height of 

 probably seventy feet. The minor or east lobe is about 400 feet 

 long and fifty feet high. The bottom of the pit, said to rest on 

 "quicksand," is cut down to about the level of Grand river 

 bottoms (1030 A. T.). The stream is here of post- Kansan age. 

 The section exposed at the main face is as follows: 



FBET. 



Loess of the usual upland or older type, character- 

 istic of the region 10 



Yellow bowlder clay with upper portion much oxi- 

 dized, leached and highly colored; lower portion 

 running into a blue with weathered joint cracks, 

 containing much weathered material and planed 

 and striated bowlders, characteristic Kansan. ... 30 



