ELIZABETHTOWN AND PORT HENRY QUADRANGLES IO3 



hematite (bog ores) ; or beds of spathic ore; any one of which in 

 the subsequent metamorphism yielded the magnetite lenses. There 

 is much apparent reason for this view. Thus the ore bodies re- 

 semble beds ; they are folded exactly as stratified rocks are ; they 

 run long distances ; and in the case of the Crag harbor, the Cheever 

 and the Pilfershire they are at what appears to be a definite strati- 

 graphic horizon, in hornblendic gneiss, a few feet below Grenville 

 limestone, and that too although they occur at intervals over a 

 distance of 4 miles, and with a mountain ridge between two of 

 them. 



The writer does not fail to feel the force of this association, and 

 the argument is a strong one. On the other hand the mineralogy 

 of the wall rocks of the ore is that of the syenite series, unques- 

 tionably shown to be intrusive in other portions of the Adirondacks. 

 The gneisses might be intrusive sheets. If they are, the apophyses 

 of similar rocks in the limestones are readily explained. The ores 

 might be basic segregations in an eruptive rock and as such they 

 might readily be drawn out into apparent beds; they might then 

 be folded like sedimentary rocks. It is a curious fact that they 

 appear in three cases in the gneisses near, although not at their 

 contacts with the overlying limestones. In other cases, as at Mine- 

 ville, no limestones are known within a mile of the ore, and from 

 one to two thousand feet of overlying gneiss have been shown by 

 the drill and the exposures. The Cheever ore is, moreover, so 

 much like the Old Bed ores at Mineville that one is disinclined to 

 think of one origin for one, and a different one for the other. 



In discussing the Mineville ore bodies these general topics will 

 be again referred to. 



No. 4. Cheever mine. This, the oldest opening in the region, 

 is situated about 2 miles or less north of Port Henry, and at its 

 eastern edge, outcrops rather more than a quarter of a mile from 

 the lake shore and about 300 feet above it. The chief workings 

 are just north of a small east and west depression, through which 

 a little brook passes into Lake Champlain, falling over a fine ledge 

 of Grenville limestone, one of the best exposures in the region. 

 There is certainly a great fault between the limestone and the 

 eastern edge of the ore, since north along the railway the limestone 

 gives way to greatly brecciated gneisses. Farther north again 

 gabbro appears, but in irregular exposures mingled with horn- 

 blendic gneisses and quite difficult to understand. The ore itself, 

 however, outcrops as a marked band or bed in green syenitic 

 gneisses, and runs to the north for nearly a mile, with occasional 



