in the Onondaga Salt-group at Syracuse, JV. Y. 143 



The geological occurrence of the Syracuse serpentine can 

 unfortunately no longer be studied, as the exposure has been 

 inaccessible for over forty years ; still some evidence of its 

 character may be derived from the testimony of observers and 

 from a study of specimens. Mr. Wilkinson, in his letter above 

 alluded to, says that an opening made only 50 feet away, on the 

 strike of this serpentine, passed entirely through gypsum. The 

 deposit is described as a horizontal bed between layers of 

 porous dolomite, but it may have been intruded in this form 

 between them as along the line of least resistance. 



It is particularly mentioned by Vanuxem that the Syracuse 

 serpentine has nowhere modified the surrounding limestone in 

 a manner that would indicate that it was once in a molten 

 state. Now, as is well-known, among all the igneous rocks, 

 peridotite is the particular one which is least liable to produce 

 contact metamorphism in the adjoining beds. Rosenbusch, in 

 his most recent work, omits all mention of this subject in con- 

 nection with peridotite, although he lays much weight upon it 

 in connection with all the other plutonic rocks. Nevertheless, 

 Mr. Diller has lately shown that the eruptive peridotites of 

 Elliott Co., Ky.. have altered to a slight degree, the shales 

 through which they break ; and I think that there is undoubted 

 evidence that the Syracuse rock did the same. This alteration 

 could not, however, be detected without the aid of the micro- 

 scope. It is now impossible to examine the action of the mass 

 as a whole, but certain specimens in my possession show plainly 

 the effect of heat upon fragments of limestone which have been 

 included in the serpentine mass. 



If the serpentine of Syracuse were eruptive we should natu- 

 rally expect to find the more granular variety near the center, 

 and the porphyritic variety near the edge of the mass. No 

 notes relating to such a distribution exist on any of Prof. Root's 

 labels, but that such was the- relative arrangement, is shown by 

 inclusions of a very fine-grained, compact, gray limestone 

 which are abundant in the porphyritic variety. Some speci- 

 mens are mere limestone breccias with a serpentine cement. 

 These inclusions are the " calcareous accretions" * of Vanuxem ; 

 and, though the line of contact between them and the serpen- 

 tine is very sharp, they show an important modification consist- 

 ing of the development in them of a greenish substance. This is 

 most pronounced near the serpentine and fades away gradually 

 as we go from it. The band is sometimes only a few milli- 

 meters wide and often has a zonal structure. One polished 

 specimen shows the line of contact with the adjacent limestone 

 (probably not an inclusion) and in this there are irregular 



* His granitic and syenitic accretions may have been foreign inclusions brought 

 up with the rock from far below the surface. 



