1896. | NEW YORK ACADEMY OF SCIENCES. 267 
drawn from it may be regarded as extremely probable, while in 
other cases much doubt remains. 
The well-known black tourmaline locality of Pierrepont af- 
fords an instance of this kind. The tourmaline, with asso- 
ciated pyroxene, phlogopite, quartz and calcite, occurs in irregu- 
lar masses in crystalline limestone. These masses are scattered 
and clearly not upon any line of contact. Nevertheless, the gneis- 
soid rock which appears at the other localities is represented 
here, appearing a few rods to the north. Itisa dark, basic look- 
ing rock ranging from distinctly gneissoid to fairly massive. 
It cannot be traced without break to the limestone, but where 
it should come in contact with the latter a much finer rock of 
a dark color appears. This fact is important, for if the gneiss 
is intrusive its marginal portion would naturally be finer. 
Sections of the gneiss show it to be made up of plagioclase and 
pyroxene, both monoclinic and orthorhombic, together with 
garnet and various accessories and alteration products. It has 
every appearance of being a somewhat metamorphosed gabbro. 
It can hardly be a mere coincidence that the minerals appear 
in the limestone just where it approaches this rock, and the 
conclusion that they have been formed by solutions set in 
circulation by the intrusion of gabbro must be regarded as ex- 
tremely probable. That tourmaline is usually formed in connec- 
tion with acid rocks might be urged in contravention of this 
conclusion (and Lacroix* regards the occurrence as a granite 
fumarole) ; but that this is not necessarily the case is shown by 
the first Rossie locality where tourmaline, like that of Pierre- 
pont, is formed on the contact zone of a diorite or gabbro. The 
two cases are, indeed, closely similar, the only marked difference 
being that at the first locality the solutions worked along the 
exact contact, while at the second they traversed the limestone 
at some distance from the intrusion. The first case would be 
considered contact metamorphism in the strict sense of the 
term; the second might be regarded as fumarole action; but be- 
tween the two it is hardly possible to draw any very definite 
line. In both cases it seems clear that heated solutions have 
done most of the work, and the exact locus of mineral growth, 
being determined by lines of least resistance to the transmission 
of solutions, must be dependent chiefly upon the character of the 
limestone. 
The question as to how far such solutions may extend their 
action is pertinent in connection with the interesting locality on 
Moore’s farm in Russell. Here the minerals are pyroxene (a 
* A, Lacroix, Contributions a l’étude des Gneiss a Pyroxéne et des Roches a 
Wernérite, p. 193. 
