202 ILLINOIS STATE ACADEMY OF SCIENCE 



would be at variance. Is cross folding known to occur 

 anywhere ? 



Displacement or faulting of the sands does not seem 

 to be shown from a study of the well logs. This hypothe- 

 sis, however, is not untenable so far as the writer knows. 

 Sufficient confirmatory evidence is lacking. 



A study of the well logs indicates the existence of 

 elongated sand lenses and bodies. This material is 

 somewhat variable, and shale or lime breaks are com- 

 monly reported within such sand bodies. 



Studies of present development fail to show these 

 transverse zones on the west side of the anticline, al- 

 though recorded dry holes indicate a fairly thorough 

 testing of the west flank. The Pennsylvanian beds are 

 more nearly flat on the east flank than on the west. Per- 

 haps this is sufficient reason either for occurrence of the 

 sand lenses or for their gathering oil. Only the higher 

 portions of such sand lenses might favor commercial ac- 

 cumulation of oil, and hence the importance of a position 

 near the crest of the anticline. Do these sand lenses indi- 

 cate near-shore phases of Pennsylvanian geography? No 

 fossils from them are available for study, but the inter- 

 spersed limestones are marine. This is demonstrated by 

 a study of samples from outcrops and from diamond 

 drill cores. Were the sand lenses formed as off-shore 

 bars, beaches, dunes, river channel fillings, or composites 

 on a delta? Eich favors the delta hypothesis for the 

 Birds Quadrangle, and it seems in harmony with condi- 

 tions to the north and northwest of that area. If this 

 were the case, was the shore line parallel approximately 

 to the LaSalle anticline as has been commonly supposed? 

 Did a large river discharge its debris into the sea in or 

 near Crawford County, and in what direction did it flow? 



Some differences of opinion are held as to the probable 

 source of the oil, but greater favor is now accorded the 

 idea of a local source and of limited migration to the 

 present sand reservoirs. Abundant organic material was 

 present in the muds (both lime and siliceous) at the time 

 of deposition, and only a small fraction of this would be 

 needod to furnish the amount of oil now known to have 

 been present. Most of the geologic section is made up of 



