WISCONSIN LEAD AND ZINC DISTRICT 553 



the state, which region is a part of the Upper Mississippi Valley lead and zinc dis- 

 trict. In this field work, which was carried on under the direction of the writer, 

 the topographic and geographic mapping of the district were conducted at the same 

 time. Each individual doing part of the mapping was furnished with a small 

 planetable, an alidade sight ruler, an aneroid barometer, and a Locke hand level. 

 Preliminary to the mapping bench-marks had been established at intervals of one- 

 fourth mile or less along the roads of the district mapped, the date for these bench- 

 marks being obtained by leveling from established bench marks of the United 

 States Geological Survey. As the roads are rarely more than a mile apart — usually 

 within half a mile of each other — the opportunity for careful topographic mapping 

 was good, and the use of the aneroid barometer was made satisfactory by the 

 ability to check on the bench-marks at short intervals of time. For general loca- 

 tions the mapping depended on the roads of the district, which usually run along 

 section lines, and on the subdivisions of the farms, which usually correspond to 

 the fractional section lines. Locations, aside from these, were drawn in by inter- 

 sections and by pacing. 



Along with the topographic work geological mapping was done, all the impor- 

 tant outcrops being located and the contacts between the different formations being 

 determined as to elevation by the barometer and in some cases by leveling. The 

 field maps were made on the scale of 8 inches to the mile, which will be reduced 

 to 4 inches to the mile on the published map. The contour interval used was 10 

 feet. The rocks of the district consist in general of undulating Paleozoics ; and 

 one important horizon, namely, the base of the Galena limestone, which is an 

 important horizon in stratigraphy as well as in the mining carried on in the dis- 

 trict, was carefully located. It is expected that the altitude of the base of this 

 formation will be shown on the finished maps by a series of contour lines. The 

 maps of this scale and detail are expected to be valuable in themselves, and it is 

 also hoped that they will give important results in working out the details of the 

 relations of the ore bodies to the geological structure of the district. 



Remarks were made on Professor Grant's paper by F. E. Wright. 

 The third paper was 



MOLYBDENITE AT CROWN POINT, WASHINGTON. 

 BY A. R. CROOK 



This paper is printed as pages 283-288 of this volume. 

 The fourth paper was 



PHYSIOGRAPHY OF THE OZARK REGION OF MISSOURI 



BY C. F. MARBUT 



The paper was discussed by C. W. Hayes, A. H. Perdue (a visitor), 

 W. M. Davis, and the author; 



