A PERIDOTITE DIKE IN PENNSYLVANIA COAL MEASURES 5 1 3 



Some 275 miles west of the Elliott Co. exposure there is a 

 similar dike in Crittenden Co., Ky. It appears in a fault, which 

 has the St. Louis beds of the Lower Carboniferous on the north- 

 west and the Upper Chester and Coal Measure beds on the 

 southeast. It strikes N. 44 p E., is known over a stretch of six 

 miles, and is more than 20 ft. wide at one place. At least one 

 other dike has been discovered in the same section. The rock 

 is a mica-peridotite, 75 per cent, of the mass being biotite and 

 serpentine from olivine. Perofskite, magnetite, chlorite, and 

 calcite make up the remainder. Some fluorspar deposits are 

 •associated with the dike. 1 



More than 300 miles southwest of the last-named exposure is 

 found the peridotite of Pike Co., Ark. This again is a biotite- 

 bearing peridotite with augite, perofskite, and magnetite. It 

 certainly cuts both Carboniferous and early Cretaceous strata 

 and is believed to have entered at the close of the Cretaceous. 2 

 In central Arkansas there are numerous basic dikes outside 

 the area of nephelite-syenite which are of peculiar mineralogical 

 composition. They are rich in biotite and augite but lack oli- 

 vine. No melilite could be identified. 3 



Leaving for the moment this review of earlier records, the 

 reader may now follow the details of the Pennsylvania occur- 

 rence, after which some general comparisons may be drawn. 



The dike which furnishes the special subject for the present 

 paper lies in southwestern Pennsylvania about thirteen miles 

 north of the West Virginia state line. It was first noted more 

 than forty years ago, by Mr. Alexis H. Ross, a local resident, 

 but it seems not to have become known to any geologist. In 

 the last few years during which coal mines have been developed 



38, 1887. Some interest has been excited in the possible discovery of 

 diamonds in this dike, and the same idea has been current with regard to 

 the Syracuse dike. 



!j. S. Diller, "Mica-peridotite from Kentucky," Amer. Jour. Sci., 

 Oct. 1892, p. 286. 



2 J. C. Branner, "Peridotite of Pike Co., Ark," Amer. Jour. Sci., July 

 1889, p. 50. Kept. Geol. Surv. Ark., II, p. 377, 1890. 



3 J. F. Kemp, "Basic Dikes Outside the Syenite Areas of Arkansas," 

 Rept. Geol. Surv. Ark., II, p. 392, 1890. 



