THE CHESTER SERIES IN ILLINOIS 301 



name Golconda may be extended to include the equivalent beds 

 in Randolph and Monroe counties. 



The lithologic character of the Golconda limestone is of such a 

 nature that its contacts with the underlying and overlying forma- 

 tions are not commonly exhibited, and at no locahty have both of 

 the contacts been observed in the same section. This condition 

 makes the determination of the thickness of the formation a matter 

 of estimate. In the neighborhood of Golconda the interval between 

 the top of the Cypress sandstone and the base of the Hardinsburg 

 is about 150 feet, and as this is the interval occupied by the Gol- 

 conda, an approximate thickness of 150 feet may be assumed for 

 the formation. The thickness of the whole of the Okaw limestone 

 in the Mississippi River counties is something over 200 feet, and 

 of this total thickness the lower Okaw, which is the equivalent of 

 the Golconda, includes approximately 150 feet, being about equal 

 to the Golconda in its typical exposures. 



Hardinsburg sandstone. — Overlying the Golconda limestone and 

 resting upon it unconformably is an important sandstone forma- 

 tion which in many places is scarcely less massive than the Cypress. 

 Butts has given the name Hardinsburg^ to this formation from a 

 Kentucky locality. In general appearance, texture, color, etc., the 

 Hardinsburg closely resembles the Cypress, and in isolated out- 

 crops not seen in relation to an underlying or overlying limestone, 

 it would not be possible in many places to differentiate the two 

 formations. The Hardinsburg, however, is somewhat less massive 

 on the whole, and includes considerable amounts of more thinly 

 bedded sandstones in places. In general the Hardinsburg is some- 

 what thinner than the Cypress, although it does have a maximum 

 thickness of at least 100 feet. There are places, however, in the 

 southern counties where the thickness does not exceed 30 feet, and 

 the average thickness is probably about 60 or 70 feet. 



In the Mississippi River counties there is no conspicuous sand- 

 stone formation which corresponds in position with the Hardins- 

 burg in the southern counties. There is present, however, within 

 the formation to which the name Okaw was originally given, a 

 horizon marked by a discontinuous sandstone layer which in 



^ Miss. Form. W. Ky. (1917), p. 96. 



