236 
GEOLOGY OF THE SECOND DISTRICT. 
they have upon the theory of the origin of the primary ore of iron, than from their importance 
in an economical point of view. The ferruginous dyke, or iron stone, is very probably an 
injected mass ; or at least most individuals who have a knowledge of the phenomena of dykes 
and veins, would not hesitate to call this ore an instance of injected matter. 
Some of the examples of the peroxide, however, have in their origin only a slight resem¬ 
blance to dykes ; those deep cylindrical masses, perforating a rock perpendicularly, are with¬ 
out doubt contemporaneous in their origin with the rock in which they are found, having been 
caught in the midst of the rock while in a soft state. The few localities of this kind of ore 
in Essex, resemble very much those in the same state of oxidation in St. Lawrence county, 
some of which I have noticed in my general account of the rocks of that district. 
Vein at Crag Harbor. 
1 shall now describe several veins, whose qualities and capabilities have been established 
by experience. 
The first is the Crag Harbor ore, situated directly upon the lake, in a cliif which almost 
overhangs it, and about fifty feet above the water. It is not far from half a mile below Port 
Henry; hence, so far as location is concerned, it is favorable, being the most accessible of 
all the veins in this mineral district. This vein is in hornblende, with which the ore is 
somewhat mixed. It is twelve feet wide, and dips southwest, or rather west, at an angle of 
thirty-five degrees. The rock at this place dips west thirty degrees.* 
This ore is black, rather compact, or subcrystalline ; it is, however, extremely tough, and 
difficult to reduce to a state of sufficient fineness for the forge. Burning or roasting suffi¬ 
ciently will do much towards overcoming this difficulty. It is strongly magnetic, though its 
polarity is feeble. Iron pyrites occurs in thin seams, but it does not appear to be dissemi¬ 
nated through the mass. Black mica occurs also in the vicinity. The specific gravity of this 
ore is 4'729 ; and it yields, on analysis. 
Protoxide of iron,. 24'50 
Peroxide of iron,. 64’80 
Silica, alumina, etc... 8"70 
100-00 
Proportion of metallic iron, 65-23 in 100 of ore.f 
This vein appears for half a mile along the lake ; and though it occurs nearer the furnace 
than some others, yet it has not proved so profitable as those more distant. The iron from 
this ore is hard and brittle, and hence for many purposes it cannot be employed ; yet it seems 
desirable that farther experiments should be made with it, for the purpose of ascertaining 
some mode by which the quality of the iron may be improved. 
The dip of the vein is often greater than that of the strata enclosing it. 
t Dr. L. C. Beck, Report of 1837, p. 25. 
