578 A. W. GRABATJ TYPES OF SEDIMENTARY OVERLAP 



Southeastward from western Virginia, the Butledge, Eogersville, and 

 Marysville formations are replaced by the Honaku limestone, a siliceous 

 limestone aggregating perhaps a thousand feet in thickness. 



The foregoing sections demonstrate that the transgression of the 

 Cambric sea, in which the strata now preserved accumulated, was toward 

 the northwest in the southern Appalachians. 



South central section. — In Oklahoma and Indian Territory the Wich- 

 ita and Arbuckle uplifts have exposed the basal Paleozoics. Here the 

 basal sandstone member, sometimes wanting, is the Eeagan sandstone, 

 varying up to 500 feet in thickness. It is succeeded by the Arbuckle 

 limestone, over 4,000 feet thick, of which perhaps the lower 1,000 feet 

 are Cambric* The following basal section occurs in the Arbuckle moun- 

 tains : 



Ordovicic 



Simpson Formation 



Feet 

 Greenish shales and thin crystalline and shelly limestones, interstratified 



with a number of beds of sandstone, one of which, near the middle 



of the formation, is from 100 to 200 feet thick. The lower division 



carries a fauna similar to the Chazy of New York and Canada, while 



the fauna of the upper division is closely related to that of the upper 



Stones River group of Tennessee and Kentucky and the Stones River 



formation of the upper Mississippi valley. Thickness 1,200 to 2,000 



Slight erosion disconformity and local deposits of pure sand. 



Cambro-Ordovicic 



Arbuckle Limestone 



Feet 

 Thinly bedded shaly limestones, with sandy beds at the top, grading 



down into light blue and white limestone and cream colored to white 

 crystalline dolomite, with occasional thin shaly strata and occa- 

 sional siliceous and cherty beds. The age of the formation varies 

 from Middle Cambric to Lower Ordovicic, including the whole of 

 the Upper Cambric and the Beekmantown formations. "From the 

 base of the formation upward to the top of the Middle Cambrian the 

 rocks are composed of thin bedded and in part intraformational 

 conglomerate and shaly limestones." This comprises several hun- 

 dred feet, while the Upper Cambric includes about 700 feet of 

 strata.f Ulrich holds that an erosion interval occurs at the top 

 of the Middle Cambric, but the evidence given for that is not con- 

 clusive. In the upper 1,250 feet fossils of the Beekmantown 

 horizon occur. Thickness 4,000 to 6,000 



* J. A. Taff and E. O. Ulrich : Professional paper no. 31, U. S. Geological Survey. 

 t C. N. Gould : Geology and water supply of Oklahoma. U. S. Geological Survey 

 Water Supply paper no. 148. 



