C. H. Smyth, Jr. — Pseudomorphs from New York. 311 



feet basal cleavage having the greatest variety of orientation in 

 different parts of the crystal. The obvious conclusion, that 

 the mica is pseudomorphous, is entirely substantiated by occa- 

 sional specimens of unusual perfection showing the crystals 

 composed wholly of mica, but having eight, instead of six, 

 faces in the prism zone, and thus reproducing the form and 

 habit of the scapolite. 



The intermediate stages in the production of the pseudo- 

 morphs of mica after scapolite are abundantly shown. Indeed, 

 most of the scapolite crystals are partially changed. As a rule, 

 the alteration proceeds from the margin towards the center, 

 but there are many exceptions, and the operation shows much 

 irregularity. 



In thin sections, the scapolite shows a strong double refrac- 

 tion and the species is probably near wernerite. Very abund- 

 ant black inclusions, probably carbonaceous, account for the 

 black color of the mineral. These inclusions often show a per- 

 fect zonal arrangement, and there is nearly always a surface 

 layer which is quite free from them. In the growth of the 

 pseudomorphs this regularity of distribution becomes obscured, 

 and there seems to be a tendency for the inclusions to become 

 somewhat segregated. As alteration proceeds, the double 

 refraction becomes very weak, the mineral takes on a rather 

 fibrous structure and the fibers have a positive optical charac- 

 ter. In this condition the mineral behaves like serpentine, 

 yields water and has a decidedly serpentinous appearance. 

 Whether this is a step towards the formation of mica, or an 

 entirely independent alteration representing different condi- 

 tions, is not evident. The latter alternative, however, seems 

 much more probable, and harmonizes better with the facts 

 observed. 



The mica, as seen under the microscope, is quite pale in tint 

 with moderate pleochroism, and shows the very low axial angle 

 of biotite, of which it is doubtless the phlogopite variety. As 

 indicated by examination of hand specimens, the mica scales 

 grow into and through the scapolite quite irregularly, with 

 every variety of orientation. 



The pyroxene associated with the scapolite has, also, a decided 

 tendency to pass over into mica, and the change is shown in 

 several sections. But, as a rule, the pyroxene has a less regular 

 form than the scapolite, and it is doubtful if any of the more 

 perfect pseudomorphs are to be referred to the former species. 

 It must be admitted, however, that a positive conclusion upon 

 this point can hardly be based upon such crude forms as the 

 pseudomorphs present. The intimate mingling of scapolite 

 and pyroxene in several sections makes it probable that some of 

 the pseudomorphs are of composite origin, in which case the 



