Tourmaline Contact Zones —Smyth. 379 
there is abundant evidence that this great formation is the 
product of a long continued series of intrusions, the diffierent 
members are so connected by every intermediate gradation, 
both of composition and of texture, and often so metamor- 
phosed, that their precise classification, lithological and chron- 
ological, is extremely difficult, and in many cases impossible. 
In the locality here considered, particularly near the shore 
opposite Alexandria bay, and in Westminster park, the larg- 
er dikes cutting the schists have all the characters of the main 
granite gneiss body. But the narrow dikes and veins have a 
markedly different nature and composition, Foliation is 
entirely lacking and the rock becomes coarser grained, more 
quartzose, ranging indeed to nearly pure quartz, while tour- 
maline becomes a conspicuous ingredient. In other words, 
these narrow offshoots take on a pegmatitic habit, though 
on a small scale. 
A striking feature is the distance they extend from the 
parent mass. A miniature pegmatyte dike, only a fraction 
of an inch in width, may cut the schists for many yards. In 
this respect and in the highly quartzose character of some 
of these dikes there is a strong resemblance to purely aqueous 
veins. 
But the most noticeable phenomenon presented in con- 
nection with the dikes and veins is their marked influence upon 
the surrounding schists. The latter rocks sometimes show 
changes similar to those described below, at the contacts with 
the main intrusive body, or with the large dikes that preserve 
the character of the main body. But these changes are small 
in amount as compared with the magnitude of the intrusion, 
and are exceptional. When, however, the narrow offshoots 
cut the schists the effect upon the latter is Mnarked, tho var- 
iable in amount. 
Along the margins of the dikes and veins the schists con- 
tain bands or irregular bunches of granular black tourmaline, 
forming a fine-grained, lustrous, black or gray rock. The 
tourmaline may be evenly distributed through the schists, or 
in bands parallel to the original foliation, the latter arrange- 
ment being very frequent. One side of a dike may have a 
tourmaline zone several inches wide, while the other side 
shows none. Again, irregular masses of tourmaline may 
