222 ILLINOIS STATE ACADEMY OF SCIENCE 



PITCH OF ANTICLINE 



The formations along the strike of the zone show locally 

 many variations. They deepen in general from La Salle 

 County southward. In places reduced pitch, flattening, and 

 reversal of pitch exist. From south Douglas County to 

 south Lawrence County (80 miles) the net pitch would 

 average 35 feet per mile. 



ROCK SECTION 



Ordovician, 



"Trenton" (Kimmswick?), 



Maquoketa or Richmond, 

 Silurian, 

 Devonian, 



Lower Mississippian, 

 Chester, 

 Pennsylvanian. 



"TRENTON" 



The Ordovician limestone, the "Trenton" of the oil-well 

 driller, which corresponds approximately to the Kimms- 

 wick and Galena, occurs under this area at varying depths 

 to the top, from 500 feet to 3,700 feet below sea level, de- 

 pending on the locations with respect to the dip of the 

 flanks and pitch of the axis of the fold. There are not suf- 

 ficient holes going through the Trenton to give any infor- 

 mation as to variation in its thickness. The upper 200 

 feet is composed of limestone. The oil production comes 

 from limestone. The highest magnesium carbonate con- 

 tent determining from two samples of the oil-producing 

 "sand" was 3 per cent. 



MAQUOKETA 



Over this whole area, the Maquoketa usually consists of 

 three members: a basal member of shale varying from 

 110 to 130 feet in thickness, a middle member of lime- 

 stone from 40 to 60 feet in thickness, and a top member 

 of shale from 90 to 100 feet in thickness. The total thick- 

 ness of the so-called Maquoketa is from 230 to 270 feet. 

 The top of the formation is reached at elevations varying 

 from 250 feet to 3,400 feet below sea level. North of the 



