274 PROCEEDINGS OF THE AMERICAN ACADEMY 



The pyroxene has been more or less changed to its characteristic 

 product; and in some instances this contains numerous seams of mag- 

 netite, as shown by a magnetized needle in scratching an uncovered 

 section. 



The feldspar crystals are in places traversed by long, slender needles 

 of apatite. The pyroxene adapts itself sharply to the contours of the 

 feldspar. 



Tlie paragenetic scheme would seem to be — 



(II.) 

 (III.) 



1. Apatite. 2. Plaoioclase. 3. Pyroxene. 



(Labradurite.) I 



The characteristic greex 



SUBSTANCE and magnetite 



as pseudomorphs. 



Pkeuxite psfudomorphs. 



(IV.) PSKfDO-AMVGDALOIDAL CHLORITE. 



after prehiiite, after plagioclase. 



Bed 800 feet E. of Hungarian lode. — The occurrence of the pseudo- 

 morphism of prehnite after plagioclase is very beautifully illustrated 

 in an extensively developed series of beds lying east of the Hungarian 

 mine. These beds are remarkable as being almost free from pyroxene. 



Tlie rock from wliich I cut my sections is brownish-gray, fine-grained, 

 with even, subconchoidal fracture. Specific gravity = 2.83. The naked 

 eye detects greenish-white, irregular bodies of prelmite, from \ inch 

 diameter down, and under (he loupe the rock is found to be thoroughly 

 impregnated with them. It also contains abundant minute grains of 

 a soft, brown mineral, intimately associated with a brilliant black 

 mineral, with metallic lustre, which is not attracted by the magnet, and 

 is probably specular iron. 



In the thin sections, the feldspar is found to have formed fully nine- 

 tenths of the primary constituents. Its sections seem to indicate square, 

 thick crystals instead of thin, tabular forms. A part of that which is 

 still transparent shows no twinning, and some sections were observed 

 in which the principal sections were parallel to the rectangular out- 

 lines, and which were probably orthoclase. The ievf optical measure- 

 ments made on random sections in the zone : n. did not give any 

 higher results than would be required for oligoclase. No pyroxene 

 was observed ; and, while it is possible that some of the soft grains 

 seen with the naked eye are derived from it, the appearances seem to 

 indicate that they are pseudomorphs after chrysolite. They generally 

 consist of a clear, slightly-greenish substance, which is in places 



