308 REVIEWS 



of at least two ages intrude this formation. Tertiary (probably) dikes 

 and stocks of monzonite porphyry and bostonite porphyry cut all of the 

 pre-Cambrian rocks. 



The mineral veins, which are the products of combined fissure 

 filling and replacement along a series of east to northeast striking frac- 

 tures, traverse both the pre-Cambrian and Tertiary rocks; they are 

 believed to be related to the monzonite intrusions. Pyritic and lead- 

 zinc veins are represented. 



A number of the specimens of the vein material show the contempo- 

 raneous origin of pitchblende, chalcopyrite, and probably minor amounts 

 of pyrite and quartz. In other specimens the pitchblende is cut by 

 veinlets of sulphides. 



"It is believed that the pitchblende was deposited during the earlier 

 or pyritic mineralization, that it was afterward fractured, and that the 

 fractures thus formed were filled by sulphides of the later or lead-zinc 

 mineralization.'' 



The pitchblende ores apparently represent a local variation in the 

 general sulphide mineralization of the area. They were formed under 

 conditions of low temperature and pressure; this is true also of the 

 Cornwall and Erzgebirge deposits. The European pitchblende occurs 

 with cobalt and nickel minerals. No such association was observed in 

 the case of the Quartz Hill pitchblende. 



V. O. T. 



Reconnaissance of the Grandfield District, Oklahoma. By Malcolm 

 J. Munn. Bull. U.S. Geol. Survey, No. 547, 1914. Pp. 83. 

 The Grandfield district includes the southeastern part of Tillman 

 County and the southwestern part of Cotton County in southern Okla- 

 homa. The purpose of the report is to discuss the geology with special 

 reference to possible oil and gas accumulations. The oldest beds exposed 

 represent the lower portion of the Wichita formation (lower Permian). 

 They consist of sandstone, shale, clay, and a clay-limestone conglomerate 

 (the Auger conglomerate lentil) which is absent in places. The Grand- 

 field conglomerate unconformably overlies the Wichita formation. It 

 is composed of well-rounded pebbles, up to three inches in diameter, of 

 quartz, quartzite, a few of granite, and fragments of chert, limestone, 

 and silicified wood imbedded in a red clay-limestone matrix. It is exceed- 

 ingly uniform in composition, appearance, hardness, and thickness 

 (average 3-4 feet), is widely exposed, and "displays a structure that is 



