OF JACKSON, NEW HAMPSHIRE. 



317 



Across the strata at acute angles, veins of granite intersect the 

 mica slate, and run north and south. The granite veins and the 

 mica slate and gneiss rocks are intersected by trap dykes running 

 northeast and southwest. 



Included in the granite veins, and passing into the mica slate, 

 occurs a vein of arsenical iron, or arsenical pyrites, which runs 

 north forty degrees east, south forty degrees west, and is from 

 one to four inches in width, and at least three hundred and twen- 

 ty-eight feet in length. This vein is cut off by the trap dyke, 

 and it was at the junction of this dyke with the vein that I first 

 noticed the occuiTcnce of crystals of the oxide of tin, associated 

 with copper pyrites, the ore being abundantly mixed throughout 

 the vein stone, which is a deep chocolate-brown mica slate, 

 deeply colored by tungstate of manganese and iron. The oxide 

 of tin in that part of the vein is highly crystalline ; and distinct 

 crystals, generally as large as a gi'ain of wdieat, are thickly im- 

 planted in it, and may be picked or washed out for examination. 

 The largest which were obtained are one quarter of an inch in 

 length, and their forms either that of the right square prism, 

 modified by numerous facets, or modifications of the primary oc- 

 tahedron, with a square base, as represented in Mohs' Mineralogy, 

 Vol. II, plate XIX, fig. 102. See p. 81. Hemitropic crystals also 

 abound, having the form as represented in fig. 2. 



1. 2. 



The color of the crystallized oxide of tin is of a deep hair brown ; 

 rarely, it is almost black. The small crystals are translucent, and 

 are, when viewed by ti-ansmitted light, of a yellowish brown 

 color. Their lustre, when free from striae, is adamantine. They 



