PAPERS OX GEOGRAPHY AND GEOLOGY 201 



Summing up the observations to date, we have the fol- 

 lowing : 



1. Robinson sand production is commonly elongated 

 in a northeast-southwest direction. This does not hold 

 true for the Chester. Perhaps correlation is at fault. 



2. These elongated areas are all east of the fold, but 

 are found very close to it. 



3. The sand top drops less rapidly from west to east 

 than to the north or south. Available data, though too 

 meagre to be very satisfactory, indicate overlapping sand 

 lenses. 



QUESTIONS 



Since these occurrences are somewhat independent of 

 the general structural conditions along the LaSalle anti- 

 cline, they raise some interesting questions. 



1. Are these transverse elongations due to cross folds, 

 faults, sand lenses, or some other agency' 



2. Wiry are" they confined to the east side of the anti- 

 cline ? Perhaps the final solution will show that they are 

 not so confined. 



3. Are they limited in occurrence to the immediate 

 vicinity of the anticline, and if so, why? 



•i. Do these occurrences suggest certain phases of 

 Paleogeography ? "What are some possibilities? 



• 5. What and where is the probable source of this 

 oil ? Is it local or may it be remote ! Has any of the oil 

 migrated very far I 



6. What is the general artesian circulation of the 

 Illinois basin? Is there a critical relation between the 

 oil accumulation and the present artesian circulation 

 through the basin ? If so. what ? 



7. How are these questions related to future explora- 

 tion ? 



SOME TENTATIVE STJGGESTK 



At present studies are too incomplete to answer finally 

 most or all of these questions, but some points seem 

 reasonably clear. 



Cross folding is not apparent here because the sands 

 appear to be missing where the synclines should be found. 

 Contours on the top and the bottom of the Robinson sands 



