348 Gihbs on Tourmalines, ^c. 



The red or rose tourmaline of Massachusetts, is found 

 chiefly at Chesterfield, in a subordinate bed of granite, con- 

 tained in mica slate. The mica slate is the predominant rock 

 of the country. It is fine grained, and contains an abundance 

 of small garnets. Direction of the strata north and south, 

 Varying a little easterly ; inclination perpendicular. The 

 bed of granite is about three hundred feet long, and from five" 

 to twenty feet broad. It is contained in a narrow ridge of 

 mica slate, which descends into, and is lost in, a valley. The 

 sides are precipitous ; the highest part is about forty feet 

 high. On the east side a considerable part of the granite has 

 been destroyed by natural causes, leaving the granite bare. 

 The granite consists chiefly of granular feldspar, with grains 

 of white quartz, and a little light coloured mica, is moderately 

 fine grained, and of a grayish white colour. In addition to 

 tourmaline, it contains also emerald, some of the crystals of 

 which are from three to five inches in diameter. I suc- 

 ceeded in getting one out of its matrix, which is three and a 

 half inches in diameter, and its summit (which is a plane 

 without any additional facettes) is perfect. 



The tourmalines are contained chiefly in a false vein of 

 silicious feldspar and quartz, which begins in the centre of the 

 upper edge of the bed of granite, and passes obliquely, de- 

 scending to the northeast, about twenty feet, where it is inter- 

 cepted from sight by the mica slate. The vein js about one 

 and a half foot thick in the upper part, and not more than six 

 or eight inches where it is lost. This vein of silicious feld- 

 jipar contains also a vein of bluish white transparent quartz, 

 which is from three to eight inches thick, and passes through 

 the centre of the vein of feldspar. 



When I first examined this rock, soon after its discovery 

 by Dr. Hunt, of Northampton, I determined the feldspar to 

 be a new variety, which has been since confirmed by Pro- 

 fessor Hauffman, and now ranks as a new sub-species, under 

 the name of siUcious feldspar. (P. 41, of the Mineralogical 

 Table.) 



