92 ILLINOIS ACADEMY OF SCIENCE. 



It is apparent that the strata can be divided into four parts, 

 lithogically. There is an upper division composed of shales and 

 sandstones and possibly a little coal ; the second division, consist- 

 ing of lighter colored dolomites; the fourth, made up of light 

 gray and bluish shales, with a little dark shale, and finally the 

 brownish dolomite. 



A detailed comparison of the first limestone of the two logs 

 shows a little similarity throughout ; both have a succession some- 

 what as follows : White dolomite at top, followed by brown dolo- 

 mite, gray-white dolomite, then a thin buff dolomite, with the 

 bottom a gray dolomite, so that there seems to be great safety 

 in the correlation of these two limestones. 



Having established the correlation of the upper limestone, the 

 lower strata fall into order. Checking the lithogical character- 

 istics of the four divisions of this well with the character of strata 

 outcropping in northern Illinois, previously described in this 

 paper, it would appear that the upper limestone is probably 

 Niagara limestone and that the Maquoketa shale and Galena- 

 Trenton limestone lie below. The Hamilton limestone does not 

 occur in these logs. The material composing the shale of the 

 first group might be Devonian or Pottsville, but the absence 

 of bituminous beds with Sporangites seems good proof that the 

 upper Devonian or Sweetland Creek shale is here absent and that 

 the strata all belong to the Pottsville. 



To summarize : We have below No. 2 or third-vein coal 250 

 feet of Pottsville sediments, 200-250 feet of Niagara sediments, 

 145-180 feet of Maquoketa sediments, and as much as 300 feet 

 of Galena-Trenton, neither well having certainly penetrated the 

 horizon. 



COMPARATIVE STUDY WITH OTHER RECORDS. 



In the comparative study of the records just summarized with 

 the records of other wells in this locality, wells Nos. 16, 31, 15, 

 14 and 13 will be included in the discussion. (See Plate II.) 



These wells are for the most part located in a linear manner 

 along the north bluff of the Illinois River, extending from La 

 Salle to Bureau (See Plate I), and they will be considered in 

 order from east to west. 



Well No. 30, Illinois Zinc Co., about one-quarter mile west of 

 well No. 16: 



