DESCRIPTION OF THE FORMATIONS. F 2 . 59 



The Clark's Mill beds. 



Overlying this is another mass of thin-bedded limestones 

 and calcareous shales in some places, perhaps generally, 

 from 100 to 150 feet thick, yielding a lime of the same 

 quality as the last, but from its less massive and more shaly 

 nature seldom opened where the other is accessible. I 

 have found but one good exposure of these beds in the 

 county. This has afforded the typical section an account 

 of which may be found in the report on Centre township. 

 (See Clark's Mill section.) A striking feature of these beds, 

 wherever exposed, is the abundance of their fossils, which 

 consequently afford the means of a full collation with those 

 of other places, especially of New York. 



The yelloic flint shale. 



Towards the top these beds become very corniferous, the 

 limestone giving place to black chert in lenticular sheets 

 often with a limestone crust. Higher still follows a thick 

 mass of shale with bands of yellow flint which I have found 

 nowhere well exposed in the county. At the same time its 

 outcrop is very well marked along the whole space between 

 the limestone and the Oriskany sandstone, and it forms in 

 connection with that next to be described the soil known 

 all over the county as "Flint-gravel." The flint lies appar- 

 ently in thin sheets which break up readily under the ac- 

 tion of frost and become bleached by the air and light, so 

 that the fields present a perfectly white surface and are 

 sometimes so thickly covered with stones that it appears as 

 if no crop could grow on it. Yet it is not unproductive, 

 but ranks high among the soils of the county. 



The white flint shale. 



Above this yellow hint shale lie two beds of white flint 

 more massive but only exposed in a few places, as, for in- 

 stance, at Half Falls mountain, near the mouth of Cocalamus 

 creek, and in the northwest of Juniata township. It crops 

 out in two beds each about twelve inches thick and sepa- 

 rated by about two feet of shale. This flint cambers the 

 fields along its line of outcrop with masses often measuring 



