The Antwerp and Fowler Belt.—Crosby. 235 
Sterling mine, two and one-half miles from Antwerp, the south 
east side of the valley is gneissoid granite and the northwest 
side is Archean limestone. The granite is of a distinctly acid 
type, of a light gray color and medium texture, rich in quartz 
and decidedly poor in ferro-magnesian minerals—chiefly biotite ; 
but with slight pegmatitic developments of only moderate 
coarseness. The granite appears to form the southeast wall 
of the dike and the limestone, in a general way, the northwest 
wall, except that in the immediate vicinity of the mine the 
dike is, superficially, bordered on the northwest side by an out- 
lier, probably of no great thickness, of the Potsdam sandstone. 
The descriptions of the mines by Putnam, in the Tenth Census 
report (vol. 15, pp. 141-144), indicate that the sandstone is a 
fairly constant feature of the deposits, occurring also at the 
Shirtleff mine in the town of Philadelphia, which is not in the 
trend of the Antwerp-Fowler belt, and probably represents a 
distinct dike or occurrence of the chloritic rock and its associa- 
ted ore. In most cases, however, the sandstone, which is still 
approximately horizontal, is described as covering the chloritic 
rock and ore more or less completely, suggesting that this basic 
igneous rock may antedate the sandstone, which was spread 
by the Potsdam sea across its outcrop; and certainly the ex- 
treme alteration of the chloritic rock is indicative of a high 
antiquity. But, on the other hand, I have observed nothing 
in the composition of the sandstone as developed at the Ster- 
ling mine confirmatory of the view that it was deposited over 
the ore-bearing formation. It is equally true, however, that 
it contains little or no identifiable detritus from the Archaean 
granite, for it is the clean, white, quartzose sandstone of fine 
and even texeure so characteristic of the base of the Pots- 
dam ; and its composition harmonizes readily with the hypothe- 
sis that it is the newest rock in the section, as indicated by its 
horizontal attitude, if we accept the view developed in my 
study of the Archaean-Cambrian contact in Colorado* that the 
transgression of the Potsdam sea over this area was so slow 
and gradual that erosion had time to accomplish its perfect 
work, base-levelling the surface and reducing all detritus to the 
two final terms—fine quartz sand and clay. Under these con- 
ditions sediments will rarely reflect in any reliable manner the 
* Bul’. Geol. Soc. Amer., 10. 141-164. ia 
