VIII 



INTRODUCTION. 



first volume of this Report, it would be superfluous to enter into 

 any extended remarks on that subject here ; but for the conve- 

 nience of those not familiar with our geology, who may use this 

 volume without always having the other directly at hand, the 

 following section, showing the order of succession, maximum 

 thickness, etc., of the strata of this State, is given : 



ILLINOIS BOCKS. 



FEET. 







150 









Tertiary 







150 







Carboniferous System. 

 , Lower ,, — Upper — , 



Carboniferous 

 period. 



Coal Measures and ) Coal, shale, clay, limestones, sandstones 



1200 





Mountain limestone 

 or Subcarbonifer- 

 ous period. 





800 







200 







150 







200 







150 





a 



B* 

 at 



X 

 CO 

 Z 

 $ 

 •a. 

 o 



« 







100 

 120 





Hamilton beds. 1 D S*£g|*' fcetedand U g hter > more P ure 





U. Helderb. period. 



Cornif. and Onondaga beds.— Gray, more or less sandy limest. 



25 



Oriskany period 





40 





Oriskany— lower beds, 1 Highly silicious, very cherty magne- 

 or Clear-creek group. J sian limest., usually in thin layers.. 



200 



Silurian System. 

 , Lower . , — Upper — . 



Lower Helderberg 

 period. 



Lower Helderberg group,") More or less magnesian and argil- 

 (D. shaly limest. of N.Y. > laceous limest., in thin layers, 



200 







Niagara group. — Magnesian and argillaceous limestones 



200 



Cincinnati period... 





140 





Trenton period 



„ , , „ . l„j„ (Magnesian, and more or less 

 Galena and Trenton beds, j p ^ re limestones 



300 





Potsdam or Primor- 

 < dial period. 





150 





Caleiferous division.— Magnesian limestones and sandstones. 



120 

 seen. 



