1C8 THE UNIVERSITY OF OKLAHOMA 



to the making of a thin section and a Fubsequent microscopic ex- 

 amination that revealed a tota' lack of the crystalline structure 

 characteristic of basalt, but instead showed a dark color, a semi- 

 opacity and a subcrystalline feature' ess texture for the most part, 

 the cnly exceptions being i few grains of metallic iron and a small 

 numl^er of very small quartz particles. 



The megascopic characteristics need not be entered into here 

 inasmuch as Pratt* and Wrather!" have quite fully considered that 

 phase in their articles. This and other examples show, however, 

 quite plainly how comparative'y easy it is to generate a so-called 

 igneous rock from a sedimentary by dynamic metamorphism. alone. 



Summary 



The above paper calls further attention to the danger of con- 

 fusing some "fused cores" or "drillites" wath igneous rocks where 

 a rotary core drill is used, contributes a complete chemical analysis 

 of a supposed "drillite," describes the petrographic features of a 

 thin section of this "drillite" and points out the ease with which 

 sedimentary rocks could be transformed into so-called igneous or 

 crysial'-ine rocks. 



XXI. NOTES ON THE BLACK MESA BASALT 



A. C. Shead 



From the Oklahoma Geolog'cal Survey. 



The basaltic cap of Black Mesa in the extreme northwestern 

 part or the Oklahoir.a Panhand'e is the eastermost occurrence of 

 that Tertiary lava flow which is so conspicuous and picturesque a 

 landscape feature in what is known as the Mesa De Maya or Raton 

 Meesa region of northeastern New Mexico, southeastern Colorado 

 and western Oklahoma. 



The abrupt, almost vertical ascent to the level tops of these 

 mesas, the straight edge of their skyline, their marked precipitous 

 relief fromi the extensive, level surface of the surrounding high 

 plains country lends particu'ar aptness to the designation of "tables" 

 apolied to this peculiar topography by the early Spanish or Mexican 

 settlers of this region. 



That portion of this flow that concerns this report, enters the 

 Oklahoma Panhandle at the western border of Cimarron county in 

 NW.>4sec. 6, T.5N., R.IE., continues east for about one-half mile 

 and thence turns northeast to the center of the north line of sec. 



*Pratt Wallace E. A note on svpposed evidence of the volcanic orgin of 

 Gulf Coast domes: Bulletin, American Association of Petroleum Geologists, 

 vol. 5 No. 1, p. 91 Jan. and Feb. 1921. 



tWrather, W. E. Supposed igreoiis rock from Wichita Cou"ty, Texas 

 wells, Bulletin, American Association of Petroleum Geologists, vol. 5. no. 4, 

 p. 512, July and Aug. 1921. 



