310 C. H. Smyth, Jr. — Pseudomorphs from New York. 



ing, however, as wollastonite is a metasilicate of simple consti- 

 tution, while scapolite belongs to the less stable class of ortho- 

 silicates and has a very complex molecular structure. 



The change of wollastonite into pyroxene is an illustration 

 of the rule, referred to below, that, throughout this region, the 

 addition of magnesia is very common in the formation of 

 pseudomorphs. 



Mica after Scapolite and Pyroxene. 



Several years ago the writer described* briefly a variety of 

 crystalline limestone, characterized by the presence of abundant 

 crystals of scapolite, which occurs near Gouverneur, JN". Y. 

 Since that time the rock has been quarried to some extent for 

 road metal and a supply of material favorable for study has 

 been afforded. The exposure is beside the highway leading 

 from Gouverneur to Hailesboro, and about half a mile south 

 of the former village. 



The scapolite is rather uniformly disseminated through the 

 limestone over an irregular area of several acres, projecting 

 above weathered surfaces, and appearing as dark patches on 

 fresh fractures. With it are associated a light-gray pyroxene^ 

 brown amphibole, titanite, a little pyrite, and an abundance of 

 rich brown mica. While this association of species is sug- 

 gestive of contact metamorphism, the irregular diffusion of 

 the minerals over a considerable area, together with the absence 

 of all zonal structure and of any exposure of igneous rocks, 

 necessitates the correlation of the minerals with the general 

 metamorphism of the region, by whatever cause or causes that 

 may have been produced. 



Sone of the minerals show perfect crystal form, but the 

 scapolite and pyroxene, with which the present communication 

 is particularly concerned, are often distinctly prismatic and 

 sometimes bounded by fairly good planes in the prism zone. 

 The crystals range in size from very small up to a maximum 

 length of about three inches. The color of the scapolite is a 

 dull grayish-black and in most cases it appears to be, at least 

 slightly, decomposed and softened. Some specimeus are, how- 

 ever, quite tough and lustrous. Close to many of the crystals 

 the enclosing limestone shows a greenish or yellowish zone 

 which looks almost like serpentine. 



The interesting feature of the scapolite is the relation it 

 bears to the associated mica. The latter mineral occurs in pris- 

 matic forms which, at first glance, might be taken for simple 

 crystals of phlogopite. But, on closer examination, it is seen 

 that each prism is a complex aggregate of mica plates, the per- 



* Trans. N. Y. Acad, of Sciences, xii, p. 213. 



