in the Onondaga Salt-group at Syracuse, N. IT. 139 



says of the Syracuse serpentine, (Final Report, p. 110): " The 

 great interest of all these metamorphic products is that they 

 have not been caused by a dry heat or fire, no evidence of the 

 kind existing ; nor is any needed to effect the change there 

 observed, though it can and has and does produce the same 

 result. All that is required is the presence of the elements of 

 the products observed at Syracuse and in a state admitting of 

 solution and of moisture, to which every degree of heat added 

 would greatly aid their mutual action upon each other ; and 

 from solution crystallization would take place, and thus meta- 

 morphic products or rocks would be formed, no igneous action, 

 commonly so called, being requisite, but a thermal one only." 

 Dr. Hunt also says after discussing this occurrence (1. c, § 34, 

 pp. 447 and 448) : " From a study of the facts before us, it is 

 apparent that we have here evidence of the formation by 

 aqueous deposition of a bed of concretionary silicate of mag- 

 nesia, taking the form of serpentine, with a little associated 

 bastite or bronzite, and probably some other crystalline sili- 

 cates.'" 



It is therefore plain that the main point of interest connected 

 with this now inaccessible occurrence of a typical serpentine 

 relates to its mode of origin. 



Through the liberality of Professor Albert H. Chester of 

 Hamilton College, the original collections of the Syracuse rock, 

 made by Professor Root while he was principal of the Syracuse 

 Academy, have been placed in the writer's hands for study. 

 This abundant and representative material, from which, how- 

 ever, the micaceous (granitic) and hornblendic (syenitic) accre- 

 tions mentioned by Prof. Yanuxem are -unfortunately absent, 

 has been subjected to a thorough microscopical examination 

 and it is the aim of the present paper to show that all 

 the facts heretofore observed and stated by former investiga- 

 tors are perfectly in accord with the igneous origin of this rock; 

 while certain other facts, h-ere mentioned for the first time, 

 place it almost beyond doubt that the serpentine was, in its 

 original state, an intrusive mass, and not an aqueous deposit. 



A macroscopical examination shows that the serpentine itself 

 is represented by two quite distinct types. One of these is a 

 very dark-green, almost black, rock, filled with minute glisten- 

 ing specks which the lens at once reveals as mica. Occasional 

 larger plates of a brass-yellow color are also seen (4 X 6 mm.), 

 and a more careful search discovers a few small masses of a 

 lighter green, more compact serpentine with a sharp crystal- 

 form. 



The second type has a lighter color than the last. It is com- 

 posed of a dense compact base which incloses numerous lighter 

 spots with a sharp crystal outline, thus producing a decidedly 



