50 GEOLOGY OF OLD HAMPSHIRE COUNTY, MASS. 



g'uished as a single individual over broad surfaces and in large disconnected 

 reticulate portions. At the line of contact of the tourmaline and the 

 anorthite many microscopic deep-red rutiles occur. 



This anorthite projection, which is a thickened part of the outer layer 

 of the "reaction rim," is separated from the olivine rock by a thick band of 

 a deep bronze-colored biotite in large scales, which is wrapped around 

 and extends beyond this projection. As it separates the gneiss at the 

 north end of the bed from the olivine rock, it may very probably be a con- 

 tinuous layer around the latter. Nothing can be seen of the lower contact. 



This biotite band, usually 4 to 8 inches thick, reaches in places a thick- 

 ness of nearly 4 feet, and incloses hard nodules of a blackish-green matted 

 hornblende and of the finest emerald-green parallel-fibered actinolite, and 

 other similar nodules which contain large, imperfect crystals of gray 

 corundum with central spots and streaks of rich sapphire-blue (see fig. 4), 

 which are wrapped in a greenish chloritic mineral of large axial angle 

 and marked pleochroism, probably clinochlore. Still other nodules contain 

 large friable masses of a fine grass-green actinolite. 



It is interesting to note how the extremely basic character of the olivine 

 rock is continued outward in the biotite-corundum rock and beyond in the 

 anorthite-tourmaline rock, and to observe how uniform this collocation of 

 minerals is in all parts of the world — a subject to which I recur after describ- 

 ing the Chester emery bed (Chapter VI). 



The broad border of decomposition products of the olivine rock men- 

 tioned above is of the highest interest, and for its understanding reference 

 may be made to the accompanying fig. 3 (p. 48). Between the biotite (p) 

 and the imchanged olivine (e) is a layer, generally about 3 feet thick, 

 which, nearer the outcrop (at the left of the figure), is 13 feet thick, and 

 consists of olivine changed in part to a pale-yellow, friable, granular 

 villarsite, and in jiart to an earthy mass of ochery appearance. Through 

 this runs an irregularly anastomosing network of veins of fibrous antho- 

 phyllite (f), which reach at times a thickness of 8 inches, at times run 

 out to extreme thinness and disappear. They are for the most part made 

 up of a woody mass of fibers, which are placed at right angles to the 

 walls of the vein and meet on a suture at the center. In the thicker 

 veins the visibly fibrous portion exists only a few inches from the walls 

 on either side, and the central portion is made up of a compact, woody 



