266 
GEOLOGY OF THE THIRD DISTRICT. 
tion or alteration, and is therefore well fitted to be a good building stone as regards durability. 
The same remarks also apply to the granite, its associate. In the third district, these two 
rocks are of contemporaneous origin. 
There are a few other aggregates met with in Lewis county, such as hornblende rock, but 
it is rare comparatively. From the boulders which are occasionally met with upon the west 
side, other rare aggregates exist, such as of coccolite and of tabular spar. These I met with 
but in one place in the county as fast rocks, namely, on the St. Lawrence turnpike about half 
way between Jefferson and St. Lawrence counties. 
The surface of the whole of the Primary region slopes to the west, about as far north as 
Black river extends through the county; beyond that point or parallel, it slopes to the north, 
the northern part being much more level than the southern part. Where it joins to Oneida at 
the southeast, it is somewhat hilly and rugged. 
Black river flows through the county upon an inclined plane, excepting at one point just 
below its junction with Moose river, where it falls sixty-three and a half feet over gneiss rock. 
From thence to Carthage, a distance of forty miles, the whole fall is but nine feet. Direction 
of the line of the mica, N. 55° E. Near the falls, is a vein of magnetic iron ore half an inch 
wide, ranging east-southeast, the only vein of the kind seen in the county. The same kind 
of ore was seen in the sands of several of the streams, and disseminated in the rock, but in 
too small a quantity to be of value ; showing the source from whence the sand derived its ore, 
and the fact of its presence. The greatest surface exposed, containing iron of that kind, was 
at the falls of Moose river, at Lyonsdale ; on the road, also, from the Natural bridge to Harris- 
ville ; and near to Lewisburg furnace. 
The most important and interesting part of the Primary region, is the north extremity, 
extending from Lewisburg to Harrisville. The greater part of it is of Primary rock, but 
showing here and there a patch of more modern origin. Like the whole of the northern slope 
of the great Primary nucleus, limestone is somewhat abundant; it forms a part of its mass, and 
without doubt there is also an intermediate deposit of it to the Potsdam sandstone. The 
magnetic, specular and red oxide of iron, so common at the east end of the slope in the second 
district, are found at the northern part of Lewis, but none yet in that abundance which gives 
to these ores a commercial value. Why that part and the east slope should be so productive 
in minerals, and the south and the west so unproductive, there are no facts yet to determine. 
The Primary limestone is found at the Natural bridge ; the rock there projects from the 
bank, and a portion of the water of the creek passes through a fissure in the limestone under 
the road, giving origin to its name : it is associated with gneiss. The limestone appears on 
the farm of Mr. Wilber, not far from the bridge ; and at another locality not far distant, where 
it was excavated for some extent in searching for lead ore, the rock containing plumbago. 
The limestone was seen in several places near Harrisville, and on the St. Lawrence turnpike, 
not far from the old toll-house. Wherever limestone exists in the third range of primary 
rocks, it generally presents numerous extraneous minerals ; being more prolific of minerals 
in this range than in the others, and the most so of any of the rocks of the Primary class. 
