the Peridotites in North Carolina. 51 



would be difficult to associate with any origin but that of an 

 intruded igneous mass, which would also account for the apo- 

 physes that have been observed shooting off into the enclosing 

 gneiss. 



At Webster, Jackson County, as shown in fig. 2, a large 

 block of gneiss is completely enclosed in such a manner by the 

 peridotites, as could be attributed only to the intrusion of these 

 in a molten condition. 



The line of separation of the peridotites and the gneisses is 

 always sharp, and there is no transitional zone from the acid 

 gneiss to the basic peridotite. Under the microscope this latter 

 rock shows the granular structure characteristic of plutonic 

 origin, the grains fitting perfectly with each other without 

 cementing material. 



The stratified appearance of "the olivine at Webster, Jackson 

 County, is readily accounted for by the pronounced evidence 

 of shearing that accompanies it. Dr. Wadsworth* has shown 

 that the evidence given by Dr. Julianf to prove that these 

 peridotites were of sedimentary origin could exist just as well 

 if the rock had an entirely different origin. 



At the Buck Creek and adjoining localities, amphibolite 

 dikes cut the peridotites or pass up through the same opening 

 with them in such a manner as to clearly indicate that the 

 peridotites occupy areas of weakness in the gneiss, through 

 which the dikes have found their exit most easily. 



Associated with all these peridotites is chromite, which 

 occurs in imbedded masses near the boundary of the lenticular 

 bodies of peridotite and as disseminated particles through its 

 borders. But at one locality, Webster, the grains of chromite 

 appear to be disseminated throughout the mass of the dunite. 

 The constant occurrence of this mineral, so characteristic an 

 accessory component of the igneous peridotites, and the almost 

 entire absence of the carbonates so commonly associated with 

 metamorphic olivine and serpentine rocks, are strong factors in 

 the proof of an igneous origin of these peridotites. All the 

 carbonates that have been observed by the author in connec- 

 tion with the peridotites are unquestionably of a secondary 

 origin. Five or six specimens of aragonite have been observed 

 at Corundum Hill, Macon County, and one at Buck Creek, 

 Clay County, intimately associated with deweylite, an altera- 

 tion product of the dunite. 



W. C. Iverr^: and C. D. Smith;}:, who spent much time in 

 the study of these peridotites rocks in the field, were both of 

 the opinion that they are of igneous origin. 



* Science, iii, pp. 4S6. 487, 1884. 



fXat. Hist. Soc. of Boston, xzii, pp. 141-149, 1852. 



\ Report of N. C. Geol. Survey, vol. i, 18T5, appendix p. 91. 



