G. H. WILLIAMS THE SYRACUSE SERPENTINE. 533 



The next paper read was on— 



OROGRAPHIC MOVEMENTS IN THE ROCKY MOUNTAINS. 



BY S. F. EMMONS. 



The paper was briefly discussed by J. S. Newberry and J. W. Spencer. 

 It is published in full among the memoirs, forming pages 245-286 of this 

 volume. 



The next communication was the following : 



NOTE ON THE ERUPTIVE ORIGIN OF THE SYRACUSE SERPENTINE. 



BY GEORGE H. WILLIAMS. 



The undisturbed Paleozoic strata of New York state are so noticeably free from 

 intrusions of igneous rocks that any occurrence whose eruptive nature can be estab- 

 lished possesses an unusual interest. Such an occurrence is the serpentine of James 

 street hill, in Syracuse, the real nature and origin of which has only recently been 

 placed beyond all doubt by new exposures made in the course of street grading. 



This rock has been known since 1837. It was described by Vanuxem and Beck in 

 the New York state reports, who regarded it as " metamorphic," but as probably not 

 produced by igneous action. Hunt bas lately brought the occurrence again into 

 prominence by citing it at great length in his "Mineral Physiology and Physiography " 

 as evidence for the origin of serpentine by chemical precipitation from aqueous 

 solutions. 



The rapid growth of the city had apparently rendered the serpentine permanently 

 inaccessible when, in the winter of 188G-'7, the writer succeeded in obtaining for 

 study a considerable series of specimens preserved in old collections. The results 

 of this purely petrographical examination (communicated to the National Academy 

 of Sciences April 20th, 1887, and published in the American Journal of Science for 

 August of the same year) were (1) the identification of the Syracuse serpentine, in 

 spite of its advanced state of alteration, as a member of the rare peridotite type 

 kimberlite, similar to those described by Lewis from South Africa and by Diller from 

 Kentucky; and (2) adducing from the structure of the rock strong evidence of its 

 eruptive origin. 



This evidence has been set forth at length in the above-mentioned paper, and need 

 not be again referred to here. The object of the present communication is to make 

 known certain new and unexpectedly acquired evidence, which places the igneous 

 origin of the Syracuse serpentine beyond a question. 



Since 1887 the digging of a deep sewer on James street and the lowering of the 

 grade of Green street, about forty rods further south, have exposed two admirable sec- 

 tions through the serpentine, which disclosed its relations to the adjacent limestone 

 and at the same time yielded an abundance of material for further study. These ex- 

 posures established three distinct proofs of eruptive origin for the serpentine in addition 

 to the internal evidence already adduced from the structure of the rock itself. These 

 three proofs are as follows: 



1. The mode of occurrence of the serpentine in the limestone. — This was distinctly 

 that of a dike, cutting perpendicularly across the nearly horizontal strata; forcing 



LXXI— Rur.T,. Grot,. Soc. Am., Vol. 1, 188'). 



