TOURMALINE AS A VEIN MATERIAL 23 



strong negative birefraction ; also a rather high index of refraction and 

 very striking pleochroism. In moderately thin sections the ordinary 

 ray is almost completely absorbed and shows a dull blackish green color, 

 while the extraordinary ra_y is light brown. 



The effect, if any, of this vein on the adjacent schist could not be ob- 

 served at the place of outcrop, but to the west of the road lie blocks of 

 schist which show a partial impregnation by tourmaline, and also a 

 gradual disappearing of the tourmaline in the direction of the cleavage 

 plane. Judging from the occurrence of tourmaline at the two other lo- 

 calities described below, it is pi^obable that these loose blocks came from 

 close contact with the quartz-tourmaline vein. 



Second Locality : Tourmaline imprec4nating Schist at Contact with 

 A large Pegmatite Vein 



This is to be found about 500 feet up the road — that is, to the west- 

 ward of the first localit3^ The outcrop is more extensive than at the 

 first named locality. It consists of a pegmatite vein about 10 feet wide 

 where it crosses the road, cutting the road diagonally with a northeast- 

 southwest strike. The tourmaline, which is to be found only sparingly 

 in the vein itself, occurs impregnating the schists at contact with the 

 vein. Just at the fence the contact may be seen well exposed. The im- 

 pregnation extends about two to three feet from the line of contact, and 

 the black streaks of tourmaline are usually parallel with the schist 

 cleavage. To the southwest of the road the pegmatite vein takes a nearly 

 north-and-south course, and continues about 10 feet wide for 200 or 300 

 feet, and then gradually widens to about double this width. On both 

 sides of the vein the schists are thoroughly metamorphosed for a foot or 

 two from the contact. They lose in places all traces of the original cleav- 

 age, and develop into aggregates of quartz and tourmaline to the entire 

 exclusion of the mica. Where this alteration is most complete the streaks 

 of tourmaline do not appear to bear any relationship to the original 

 cleavage direction. Curiously enough, as the vein widens the tourma- 

 linizing of the schist becomes less and less marked, till it ceases alto- 

 gether where the vein ends suddenly at its widest point. 



Fragments of this tourmalinized schist are thickly strewn along both 

 sides of the road, and the varying structures may be well studied from 

 these fragments. In general, the rock may be said to present the appear- 

 ance of a laminated or banded grayish or reddish gneiss, and without 

 close observation one would hardly suspect the presence of tourmaline. 

 Usually the banded schistose structure is sharply defined and the bands 

 straight and parallel, but not infrequently a decided crinkling of the 

 bands is to be observed similar to that noticed in the neighboring mica- 



