126 IOWA ACADEMY OF SCIENCE 



whose direction the work has been carried on and whose advice 

 was most valuable because of his intimate acquaintance with 

 numerous localities in the Driftless Area. 



FORMER WORK DONE. 



For the past twenty years geologists who have worked in the 

 Driftless Area have noticed the broad stretches of upland sur- 

 face lying at approximately the same levels and harboring a 

 civilization quite distinct from that of the deep, gorge-like valleys 

 below the upland levels. In many cases the upland flats are so 

 conspicuous as to be known locally as "prairies" on which are 

 located villages, woodland areas, main roads, and many square 

 miles of flatfish, rolling country. These striking features have 

 been described in the reports, barely receiving mention in some, 

 whereas in other cases they have been treated as fully as avail- 

 able data permitted. It is not surprising that different men, 

 working independently, at different times, and in widely sepa- 

 rated, ,portions of the Driftless Area did not round out their 

 combined work into the harmonious whole. Accordingly, when 

 an attempt is made to build the blocks as worked out into a unit, 

 the wide divergence of conclusions is emphasized. The results 

 of some of the most important work done and the geographical 

 location of this work is shown is figure 10. For more detailed 

 accounts of this work, see the brief bibliography following. 



BIBLIOGRAPHY. 



Bain, H. F., Zinc and Lead Deposits of Northwestern Illinois: Bull. 

 U. S. Geol. Survey No. 246, pp. 13-16. 



Calvin, Samuel, Geology of Allamakee County: la. Geol. Survey, Vol. 

 IV, pp. 41-44. 



Grant and Burchard, Lancaster-Mineral Point Folio: U. S. Geol. Sur- 

 vey, pp. 1 and 2. 



Hershey, 0. H., The Physiographic Development of the Upper Missis- 

 sippi Valley: Am. Geologist, Vol. 20, pp. 246-268. 



Howell, J. V., The Occurrence and Origin of the Iron Ores of Iron 

 Hill, near Waukon, Iowa: Iowa Geol. Survey, Vol. XXV, pp. 33-69. 



Leonard, A. G., Geology of Clayton County: Iowa Geol. Survey. Vol. 

 XVI, pp. 220-233. 



Salisbury, R. D., Preglacial Gravels on the Quartzite Range near 

 Baraboo, Wisconsin: Jour. Geology, Vol. Ill, pp. 655-667. 



Salisbury, R. D., and Atioood, W. TV, The Geography of the Region 

 about Devils Lake and the Dalles of the Wisconsin: Bull. No. V, 

 Wisconsin Geol. and Nat. Hist. Survey, pp. 60-64. 



