1890.] NATURAL SCIENCES OF PHILADELPHIA. 119 



It will be instructive in this connection to quote observations of 

 of Dr. Genth and others in regard to these and like serpentines. 



Speaking of tlie corundum of Chester, Mass., Dr. F. A. Genth' 

 says : 



" The whole deposit lies in a talcose slate and serpentine between 

 gneiss and mica slate in the centre of the Green Mountains." 



Dr. Genth ^ shows that the chromiferous and nickeliferous ser- 

 pentines and talc slates owe their existence to the decomposition of 

 chrysolite rocks. 



" In Pennsylv.inia, where the unaltered chrysolite rock has never been observed, 

 a rock has been found which is its representative and contains the same constituents, 

 only in different proportions. In Nortii Carolina the granular chrysolite always 

 contains small quantities of enstatite (bronzite), in Pennsylvania on the contrary we 

 have an enstatite (bronzite) rock containing small grains (from 5 to 10^) of chrys- 

 olite. It is best developed at Castle Rock, Delaware county, also near Wood's 

 Chrome Mine in Lancaster county. 



In all the chrysolite rocks small grains or crystals of chromite are disseminated 

 through the mass of the rocks; in the serpentine, which has resulted from (he 

 alteration of the chrysolite, these crystals or grains are still present and give evi- 

 dence of the original mineral " ■* 



Dr. Julien * writing of the dunyte beds of Is . C.says, "the dunyte 

 beds are everywhere and exclusively found inclosed in a stratum of 

 hornblende gneiss black and slaty. This forms the upper layer and 

 largely occupies the central zone of the mass of gneisses and schists 

 entirely of types identical with those found in the White Mountains 

 of New Hampshire." 



Dr. R. W. Raymond, '' speaking of the Jenks corundum mine in 

 Macon Co., N. C, and quoting Prof. Kerr says, " This mountain tract 

 of Laurentian rocks ^ =!^ * along the middle of the belt now 

 specially under consideration a discontinuous line of outcrops 

 appears at intervals from Cane creek in Mitchell county through 

 the intervening counties of X. C. into Union county, Ga. These 

 are called in the State Geological Report dykes of chrysolite or 

 dunite," and adds, " I should not be surprised if future careful study 

 of all the localities should show these chrysolite beds to be inter- 

 calated members of the formation in which they occur." 



He then concludes as a result of his studies that the rock is un- 

 doubtedly sedimentary in character, the dunyte sometimes inter- 



1 Am. Phil. S.. September 19th, 1873. 



2 Sill. Jour. Vol. 2, pp. 111-202. 



3 Dr. Genth, Am. Phil. So., Aug. ISth, 1882, page 394. 



4 Proc. Boston Soc. of Natural History, Vol. XX, p. 11, Dec. 6th, 1882. 



5 Trans. Am. Inst. M. E. 1876. 



