STRATIGRAPHIC SUMMARY. 617 



Middle Ordovicic. 



Black River or Carter's Creek limestone. 80 ft. 

 Stones River 360 ft. 



comprising : 



Glade limestone. 

 Ridley limestone. 

 Pierce limestone. 

 Central limestone. 



The base is formed of the Upper St. Peter horizon. 

 In western Tennessee (Columbia quadrangle) the Ordovicic has 

 been subdivided as follows: 



SUPERFORMATION. 



Lower Siluric — Clifton limestone 60 ft. 



(disconformity) 



Upper Ordovicic. 



Fernvale formation o- 40 ft. Richmond. 



(disconformity) 

 Leipers formation o-ioo ft. Lorraine. 



(disconformity) 



Catheys formation o-ioo ft. "| 



Bigby limestone 30-100 ft. L Trenton. 



Hermitage formation 40- 70 ft. J 



(disconformity) 



Middle Ordovicic. 



Carters limestone.. 40- 60 ft. Black River 



Lebanon limestone. 70-100 ft. Upper Stones River. 

 (Base not shown.) 



In the Rio Grande region of New Mexico and Texas, the 

 Ordovicic comprises a lower division, the El Paso limestone (1,000 

 ft.) and an upper, the Montoya limestone (250 ft.). 



In the Arbuckle Mountain region of Oklahoma, the Upper 

 Arbuckle limestone represents the Lower Ordovicic, the Middle 

 being represented by the Simpson formation and the Upper by the 

 Viola limestone and Sylvan shale — though the latter may be basal 

 Siluric. 



