1877.] 229 [Wadsworth. 



augite and viridite, and the great amount of the biotite in the more 

 decayed portions of the rock and the resulting sand. A silvery white 

 to greenish white mica is found in very thin scales in the rock, and 

 from its pyrognostic characters is probably biotite, or a related mica. 



The apatite is found in long, rounded and hexagonal needles, pen- 

 etrating both the augite and the feldspar. In general it is unaltered, 

 but in a few cases its cracks are filled with viridite. 



The hornblende of the reddish feldspathic veins is in long, black 

 prisms closely resembling the augite, and undergoes similar altera- 

 tions. Uralite is found in small quantities. Calcite occurs in veins 

 lining fissures, and in connection with the prehnite. Quartz is 

 found chiefly in nodules and in irregular masses partially filling inter- 

 spaces between the feldspar, in the coarser veins. It is not, however, 

 an essential constituent of any part of the rock. 



The prehnite occurs in veins lining fissures in the rock, also form- 

 ing pseudomorphs after the feldspar and augite, principally the 

 former, particularly near the veins containing prehnite, where the 

 feldspar is partially or wholly replaced by it, as well as in the coarser 

 parts of the rock, and near its junction with the slate. The partial 

 alteration of the feldspar to prehnite appears to extend through con- 

 siderable of the massive part of the rock, and gives rise to much of 

 the greenish color of the feldspar when it has not been changed to 

 viridite. 



Chalcodite, which has only heretofore been found at the Sterling 

 Iron Mine, Antwerp, N. Y., I have found in some abundance in this 

 locality. It occurs in masses and pseudomorphs made up of minute 

 flakes, and also in stellated groups. 



Two varieties are found, one of a green bronze color, which on 

 heating in a closed tube yields water and turns yellow, the other of a 

 yellow bronze color. The first variety occurs on the interior, and in 

 parts that have not been as directly exposed to atmospheric action as 

 the yellow variety. The genesis appears to be as follows: the altera- 

 tion of the original minerals to viridite, then the passage through the 

 green bronze to the yellow bronze state, that being probably the 

 chalcodite proper. In physical, pyrognostic and chemical characters, 

 it closely agrees with the descriptions given by Professors Shepard 1 

 and Brush 2 of the Antwerp mineral, therefore it is not necessary for 

 me to give those characters here. It takes the place of the augite, 



1 Proc. Am. Association Adv. Science, Yol. vi, p. 232. 



2 Am. Jour. Science, 2d Ser., Vol. xxv, p. 198. 



