266 GEOLOGY OF THE THIRD DISTRICT. 



Uon 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 modem 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. 



