OIL AND GAS IN THE CENTRAL BASIN. 



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ones to the surface in that 

 locality. The Ridley lime- 

 stone and the Murfreesboro 

 limestone are separated only 

 by the Pierce shale, which is 

 a thin formation, less than 30 

 feet thick, and like the other 

 two, is in most places covered 

 with soil. Where this is ex- 

 posed it can easily be recog- 

 nized, but the Ridley lime- 

 stone and Murfreesboro lime- 

 stone are so much alike that 

 it is difficult for even the geol- 

 ogist to distinguish them ex- 

 cept in places where they can 

 both be seen, with the Pierce 

 shale between them. In such 

 places, it is known that the 

 limestone above the shale is 

 Ridley, and that below is 

 Murfreesboro. 



It must not be supposed 

 that the rock beds dip off uni- 

 formly from the highest part 

 of the arch, like the surface 

 of a very flat dome. Rather, 

 they are in small, wave-like 

 folds, the beds here passing 

 downward, forming troughs, 

 and there upward, forming 

 arches. From the somewhat 

 limited investigation made by 

 this survey, it appears that 

 none of these folds are long, 

 but die out in short distances 

 and are succeeded by others, 

 giving the whole structure a 

 wobbly form. 



