94 ILLINOIS ACADEMY OF SCIENCE. 



vicinity of La Salle, within a distance of one-quarter of a mile 

 relief as great as 200 feet. A third point brought out by the 

 chart relates to the source of the water supply. It is seen that 

 almost all the wells obtain water not from the St. Peter sand- 

 stone, but from the Galena-Trenton limestone, a condition which 

 has not been generally recognized heretofore for this part of the 

 State. 



For the sake of comparison, the log of a well recently drilled 

 at Deer Park, which lies on or just east of the anticline, appears 

 as No. 28, plate 11. The succession shown by this log is very 

 different from that shown in the logs to the right. The upper 

 limestone, of which only a part is left, is the Trenton limestone 

 outcropping along the banks of the Vermilion River. Below this 

 lies about 200 feet of St. Peter sandstone. This is followed by 

 180 feet of Lower Magnesian or Shakopee limestone. This lies 

 above a rather massive sandstone of about 200 feet in thickness, 

 probably the New Richmond sandstone. The well penetrates 

 about twenty feet of limestone below the New Richmond. 



A further reason for introducing this log is for the sake of 

 showing the difference in the stratigraphic conditions on the two 

 sides of the anticline, and the possibility of confusing the St. 

 Peter sandstone and New Richmond sandstone. East of the 

 anticline the upper sandstone is eroded in the Illinois River bot- 

 tom about Utica, hence the lower sandstone is often reported as 

 St. Peter. Furthermore, the record of this well shows us the 

 character of strata that would probably be encountered in deeper 

 drilling west of the fold. 



PLATE III. 



In order that the local condition existing in the vicinity of 

 La Salle may be more clearly understood, a cross-section has 

 been prepared, extending from Rock Island to Joliet, showing 

 structural conditions in northern Illinois, and the stratigraphical 

 conditions from the Lower Magnesian formation to the "Coal 

 Measures." The source of the data shown on this chart is 

 partly from published articles by Dr. Udden, including the 

 World's Fair cross-section and the Rock Island section in the 

 seventeenth Annual Report of the Federal Survey, and partly 

 from data in the files of the State Survey. 



To sum up briefly what it is desired to show by the chart: 

 ti) The general occurrence of the same strata having somewhat 

 the same thickness on the two sides of the anticline, so far as they 



