LOESS AND THE IOWAN DRIFT. 359 



the loess-series is found, as stated, in the fact that the line 

 between the lower deposit and the loess is not always sharp. 

 It should not be inferred from this, however, that there is 

 great indefiniteness or confusion along- the dividing- line. This 

 line is often quite sharp, but even in the cases in which there 

 is a blending, the complete transition takes place usually 

 within a vertical distance of from one to three inches. This 

 blending does not indicate a unity of origin as has been as- 

 sumed, and is entirely consistent with the seolian hypothesis 

 of loess-origin, as has been indicated on p. 341 of this Bulletin, 

 and as may be determined by the study of soil-accumulation 

 in sand-dune regions. The inter-lamination of sand and loess 

 has been observed only where fLie sands underlie the loess, 

 and suggests an original sand-dune area which would become 

 covered with soil-retaining vegetation for a time, but in which 

 sand-dune conditions were occasionally restored, perhaps dur- 

 ing periods of protracted drouths, the soil (loess) and sand thus 

 alternately occupying the surface. A fine example of inter- 

 lamination may be seen along the Cedar Rapids & Iowa City 

 electric line, near the north line of section 27, T. 81 N., 

 R. 7 W., in Johnson county, Iowa. Here the alternating bands 

 have a total thickness of several feet, six feet being exposed 

 in the cut. The largest loess-band measures two feet in thick- 

 ness, and is fossiliferous. The remaining layers of sand and 

 loess are mostly from one-eighth to two and one-half inches 

 in thickness. No pebbles were found, and the fossils occur 

 only in the loess. An interesting fact in connection with this 

 deposit is the proximity of sandy areas (low sand-dunes) bor- 

 dering the broad river valley to the west and joining with the 

 ridge through which this cut passes. In portions of this area, 

 within the recollection of the writer, there have been such 

 alternating changes in surface conditions, the sandy prairie 

 being sometimes covered with soil-retaining vegetation, and 

 again with shifting, wind-blown sands. Professor Cowles 

 similar'y reports "many fossi! soil lints .... on the Seeping 

 Bear dunes at G'en Haven, Mich."* 



*Bot. Gazette, vol. xxvii, p. Ill, 1899. 



