LA SALLE COUNTY. 47 



Feet. 



No. 7. Nodular shale, or shaly limestone 6 



No. 8. Upper main limestone 12 



No. 9. Green shale 2 



No. 10. Lower limestone 10 to 12 



These are the highest Coal Measure strata outcropping in the 

 county, and they have been referred by some observers to the 

 Permian age, but I was unable to find any satisfactory evidence of 

 unconformability between them and the limestone No. 8, on which 

 they rest, and the fossils, so far as they have been determined, are 

 of well-known Coal Measure forms. 



The most common fossils in the calcareous shales and impure 

 limestones of this horizon were the following species : Orthis Pecosii, 

 Chonetes Flemingi, Productus La Sallensis, Hemipronites crassa, Athy- 

 ris subtilita, all of which are characteristic Coal Measure forms. 

 On the south side of the Illinois, these beds make their appearance 

 in the cut of the Illinois Central railroad from the river bluff to a 

 point half a mile or more beyond Oglesby, where the railroad grade 

 finally ascends entirely above them and onto the overlying drift 

 deposits. 



The beds immediately below the main limestones are well ex- 

 posed in the bluffs between La Salle and Peru, and there is a de- 

 cided increase in the thickness of the shales as we recede from the 

 axis of disturbance, already mentioned on a preceding page. On the 

 Little Vermilion where it intersects the bluffs of the Illinois, the 

 main limestones are separated by only about two feet of greenish- 

 colored shales, but in descending the river bluffs toward Peru, the 

 shale increases to a thickness of 8 or 10 feet. The following sec- 

 tion was made along the river bluff in the vicinity of Peru : 



Ft. In. 



No. 1. Upper limestone 10 to 12 



No. 2. Green and purple shales 6to 8 



No. 3. Lower division of main limestone 6 to 8 



No. 4. Bituminous shale 1 6 



No. 5. Gray, brown and green shales 8 



No. 6. Impure coal 



No. 7. Gray and green shales 12tol5 



No. 8. Nodular limestone 4 to 5 



No. 9. Green nodular shale 12tol5 



No. 10. Hard gray limestone 2 to 3 



No. 11. Green shale (exposed) 2 



No. 12. Unexposed to river level 15 to 20 



No. 1 of this section is the main quarry rock used as a building 

 stone in LaSalle and Peru. It is a compact gray limestone, con- 

 siderably stained with the oxide of iron, and resembles the limestone 



