234 The American Geologist. sa 
visited the Sterling mine, in company with Capt. Hodge, an in- 
telligent resident of Antwerp and for many years superinten- 
dent of the mine, and a party of students, I was surprised, not 
having previously read up on the geology of the mine, to find 
that the ore occurs in, and in intimate association with, a mas- 
sive, soft, greenish-black, chloritic-looking rock, which is di- 
vided in all directions by slickensides and appears to be a high- 
ly altered (chloritized) trap. It appears that this rock was 
called serpentine by Ebenezer Emmons.* In part it bears some 
icsemblance to serppentine, but in general the aspect 1s chlor- 
itic rather than serpentinic. Being fresh from the study of the 
deposits of nickeliferous pyrrhotite and chalcopyrite in the di- 
oritic rocks of the Sudbury district in Ontaroi and of 
the Gap mine in Lancaster county, Pennsylvania, which 
had been quite clearly. shown by Kemp and others to 
be products of magmatic differentiation, I at once adopted 
this as a provisional explanation or working hypothesis 
for the deposits of the Sterling mine, and probably of the other 
mines of the Antwerp-Fowler belt, Capt. Hodge having assured 
me that the geological conditions were similar throughout this 
linear series of deposits. 
At the time of my visit, all of these mines had been closed 
for some time, probably never to be reopened ; but my observa- 
tions on the surface, including the dumps, supplemented by 
such information concerning the underground conditions as the 
superintendent could give me, led me to the conclusion: that the 
ore-body of the Sterling mine is in a dike, fifty feet or more 
in width, of some highly altered basic rock, possibly diabase; 
that the ore was originally a magmatic segregation of this rock, 
chiefly in the form of sulphides, which have subsequently suf- 
fered more or less complete oxidation to a considerable depth, 
the ore being now, virtually, a gossan; and that this dike is, 
probably, continuous for the entire length of the belt of mines, 
although absolute continuity is by no means essential to the hy- 
pothesis. 
The trend of the ore-belt and the hypothetical dike is ap- 
proximately northeast from the vicinity of Antwerp, closely fol- 
lowing the valley of a tributary of the Oswegatchie river. At the 
* Geology of the Second District, pp. 93-96. 
