142 G. H. Williams — Serpentine {Peridotite) occurring 



The occurrence of perofskite in the Syracuse serpentine is 

 in all respects identical with that in the rocks described by 

 Boricky, Hussak and Stelzner, specimens of which have been 

 carefully examined for comparison. It is interesting as being 

 the first instance on record of perofskite as a constituent of any 

 American rock, and also as the first discovery of perofskite in 

 a peridotite or serpentine from any locality. 



The porphyritic type of the Syracuse serpentine is essentially 

 identical with that above described in all points except its 

 structure. The groundmass is finer grained, which throws the 

 characteristic crystal-forms of the olivine and enstatite into 

 a sharp relief. The structure of this rock is represented 



in the accompanying figure. The octahedral crystals are much 

 smaller than in the other rock and are confined wholly to the 

 groundmass. The brown mica is here much less abundant. 

 The porphyritic olivines especially are most representative 

 examples of the well-known serpentine pseudomorphs, so often 

 described and figured by Tschermak and others in eruptive 

 rocks. They are sometimes stained deep red by iron oxide, 

 which occasions the above-mentioned blood-red spots. 



The persistence of structure in this rock, in spite of the pro- 

 foundest chemical changes, is remarkable. In one porphyritic 

 specimen the groundmass is almost all carbonate, the mica has 

 become quite colorless, and the olivine crystals are changed to 

 a perfectly isotropic, colorless substance, enclosing the sharpest 

 possible rhombohedra of dolomite ; in fact none of the original 

 components remain except the chromite, and yet the structure 

 is just as sharp and characteristic as in the specimen above 

 figured. 



