402 STUART WELLER 



places it is considerably less, perhaps being as thin as forty feet in 

 places. The average thickess of the formation throughout its 

 entire extent is approximately seventy feet. 



Clore limestone. — The Clore limestone was first described in 

 Randolph County^, and at the time it was believed to be the highest 

 formation in the Chester series, but later observations have shown 

 that it is succeeded by still another sandstone, and this again by 

 a higher limestone formation. In many places the Clore really 

 includes a larger amount of shale than it does limestone, locally 

 the shale being much in excess of the limestone, and some ledges of 

 the limestone itself are more or less shaly. The limestone beds of the 

 formation exhibit a considerable amount of variation, some being 

 compact and fine grained, others being shaly, some are hard and 

 apparently siliceous, and a. few beds are more or less crystalline. 

 Nearly all of the limestone beds are more or less impure. The 

 shale beds are almost entirely argillaceous or are more or less cal- 

 careous, the more calcareous beds having thin, platy layers of 

 limestone imbedded in the shale. In the Mississippi River counties 

 there is apparently a greater amount of limestone in the forma- 

 tion than in the southern counties, but wherever the formation 

 occurs it is difficult to determine in detail its true composition, 

 because of its non-resistent character and the consequent covering 

 of surficial material. 



The Clore is not a thick formation. Its thickness in two 

 measured sections in the Mississippi River bluffs below the mouth 

 of Marys River is between thirty and forty feet. In places, where 

 it is the uppermost formation in the Chester series, it varies in 

 thickness from forty feet down to nothing, due to the erosion of 

 the higher beds. In the southern counties of the state the Clore 

 is nowhere the highest formation of the Chester, and its lower and 

 upper limits can rarely be determined with exactness. Further- 

 more both the lower and upper limits of the formation have 

 nowhere been determined in one and the same section with any 

 degree of accuracy. These conditions make the determination of 

 the thickness of the formation in these counties rather uncertain, 



^ Weller, Trans. III. Acad. Sci., Vol. VI (1914), p. 129; also ///. State Geol. Surv., 

 Monog. I (1914), p. 29. 



