1896. ] NEW YORK ACADEMY OF SCIENCES. 263 
The mineral composition and structure of the rock revealed 
by the microscope would be sufficient to establish its igneous 
nature in the absence of all supporting field evidence. <As 
it is, the proof is complete. This leads at once to the con- 
clusion that the minerals of this locality have been formed by 
contact metamorphism, where an intrusive rock of intermediate 
composition breaks through a limestone. All of the phenomena 
are so clearly exhibited that it seems impossible to arrive at any 
other conclusion, and the locality is, for this reason, of much 
importance as a standard of comparison. At the same time, the 
bedded aspect of the intrusive, its gneissoid character, and the 
great variation in the width of the contact zone, all point out 
lines along which the phenomena might be so modified as to in- 
troduce much obscurity in the relations of mineral occurrences 
of like origin. 
The last mentioned point, in particular, needs further consid- 
eration. As stated above, the mineral body is part of a zone 
which follows the contact of the diorite and limestone. But 
through most of its extent this zone is very narrow, ranging froma 
few inches down to almost complete disappearance, and consist- 
ing of a fine coccolitic mass, instead of the large crystals of the 
main body. To account for such wide variation in the amount 
of mineral development, it seems necessary that there should be 
corresponding variation in the rocks involved, or in some other 
factor in the process. ‘The first proposition can not be admitted, 
as both the diorite and the limestone are entirely too homo- 
geneous to allow the required amount of variation. The alter- 
native raises the question as to how much of the contact action 
is due to heat alone,and how much to the effects of heated 
solutions and gases. This question seems to be quite definitely 
answered by the phenomena of occurrence already described. 
The narrow band of coccolitic material which marks the whole 
contact may well be the result of heat acting upon the limestone, 
accompanied by a slight transfusion of material from the diorite. 
but without the intervention, to any great extent, of other 
agents. But it is very difficult to account for the sudden ex- 
pansion of the belt intoa large mass of finely developed min- 
erals, unless it has resulted from a concentration, et this point, of 
heated solutions rich in mineralizing agents. 
As to the cause of this concentration, it is impossible to come 
any closer than to say that, doubtless, there was here a line of 
minor resistance which afforded a channel for the transmission 
of the solutions. That the mineral mass could not result from 
the rearrangement of materials in the limestone is apparent from 
an examination of the latter rock. It is a fairly pure mass of 
