[Annals N. Y. Acad. Sci., Vol. XVII, No. 4, Part II, pp. 509-518, 

 August, 1907.] 



A PERIDOTITE DIKE IN THE COAL MEASURES 

 OF SOUTHWESTERN PENNSYLVANIA. 



By J. F. Kemp and J. G. Ross. 



The discovery of dikes and other forms of intrusive rocks in 

 the almost undisturbed Paleozoic strata west of the Appalachian 

 upheavals is a. matter of much scientific interest and has been 

 so esteemed in the several announcements which have been 

 hitherto made. The occurrences are all in localities where, 

 under ordinary circumstances, intrusive rocks would not be 

 anticipated, and they tend to make a geologist cautious in 

 inferring the necessary absence of igneous phenomena beneath 

 any region from the mere fact that they do not appear on the 

 surface. By way of introduction to a new occurrence it will be 

 of interest to recapitulate briefly with the accompanying outline 

 map the cases already known. 



The first three discoveries were mentioned by Lardner 

 Vanuxem in his report on the Third District of New York in 

 1842, although one of them, the Syracuse Serpentine, had been 

 noted five years before. 1 The serpentine, however, was not 

 recognized as igneous in its nature, until the microscopic exam- 

 inations of Professor Geo. H. Williams demonstrated its true 

 character in 1887. Since then other neighboring occurrences 

 have been discovered from time to time and have been described 

 in the citations given below. Speaking in general terms, the 

 rock is a peridotite and penetrates the Onondaga Salt Group. 

 In some more recently afforded material C. H. Smyth, Jr., has 

 identified melilite, and it is possible that this mineral was once 



>For a full account of this interesting rock and a sketch of its history 

 in the literature see Geo. H. Williams, "On the Serpentine (Peridotite) 

 Occurring in the Onondaga Salt Group at Syracuse, N. Y.," Amer. Jour. 

 Sci., Aug. 1887, p. 137. 



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