OKLAHOMA ACADEMY OF SCIENCE 109 



33, T.6N., R.IE., a total distance of about three miles within this 

 state. Since the average width is about one-half mile, according lo 

 E. P. Rothrock,* the area covered by the flow is about 1.5 square 

 miles in Oklahoma. The author just cited gives the average thick- 

 ness of the flow within this area (Cimarron county) as about 58 

 feet, varying from 50 feet thick two mi'e? north of Kenton, Okla- 

 honja, to 65 feet at Nigger Spring. From the figures given the ton- 

 nage of this rock within the Oklahoma borders can be easily com- 

 puted. 



To give a more general idea of the nature of the associated 

 formations it is thought fit to include the following section by 

 Charles N. Gouldf before passing on to the more specific minor 

 physical and chemical peculiarities of the rock. 



Section of Black Mesa, two miles north of Kenton, Oklahoma. 



"Malpais" basaltic lava 100 feet 



Tertiary Tertiary pebbles 20 feet 



Dakota Heavy massive sandstone, crossbedded 45 feet 



Clay shale 40 feet 



Massive crossbedded sandstone, smaU rounded 



concretions _ 60 feet 



Shale, yellow and black, talus slope 100 feet 



Sandstone, gray and reddish 70 feet 



Red Beds Red Clay 103 feet 



This section gives some idea of (1) the thickness of the rocks, 

 (2) the general nature of the underlying sedimentaries of the region 

 and (3) the amount of erosion that has taken place in this part of 

 the country since the Tertiary in which the basalt was extruded. 



Probably the most prominent structural feature of the rock en- 

 masse is the vesicularity. This feature is strictly subordinate in 

 the lower half of the rock where the basalt is quite dense but the 

 porosity increases progressively from about the middle of the flow, 

 to the surface where the vesicles are at a maximum in number, 

 and size, while the density is at a minimum here. It is thus possi- 

 ble to locate a given specimen from the mass quite definitely. 



The jointing in the rock is not marked which is a feature to 

 be expected by reason of the conchoidal fracture that is developed. 

 The other major physical features are those common to most 

 basalts, namely, the color is srayi'sh black, the surface scoriaceous 

 and the structure porous. 



*Rothrock E. P. The Geology of Cimarron County (Unpublished thesis). 

 tGoUd Charles Newton. Geology and water resources of Oklahoma: 

 U. S. G. S. Water-Si:pply Paper 148 p. 82, 1905. 



