REPORT OF THE DIRECTOR I9II 145 



would be suggested, the pyrite being a probable primary constituent, 

 concentrated by magmatic differentiation. As shown below, this ex- 

 planation is, at first glance, strongly suggested for one of the chief 

 deposits but further study indicates that it is inapplicable even here, 

 while as a general explanation of the rusty gneisses it has no claim 

 to consideration. 



For the present it may be assumed that the rusty gneisses are of 

 sedimentary origin, representing shales and sandstones interbedded 

 with the limestones of the Grenville sea. 



With' this brief introduction, the different mining localities may be 

 described, taking them in order from west to east, and in each case 

 first stating the facts observed in the field and then giving the 

 leading megascopic and microscopic features of typical specimens of 

 ores and wall rock. The paper closes with a general discussion of 

 the problem of genesis. 



THE COLE MINE 



The Cole mine, situated about four miles north of Gouverneur, 

 was idle when visited by the writer, but has since been started up 

 again and is likely to be an important producer. Rock exposures 

 around the flooded pit were not extensive but sufficient to show the 

 usual strongly foliated rusty gneisses, the more pyritiferous parts 

 of which constitute the ore. Beneath this is a mica schist, and still 

 lower down, with a gap of five or six hundred feet in outcrops, is a 

 beautiful serpentinous limestone; Thus the rocks are distinctively 

 Grenville in type and, as a matter of fact, the location is in the midst 

 of one of the most extensive of the Grenville limestone belts of the 

 region. The only recognizable igneous rock associated with the ore 

 is pegmatite which occurs in small patches and strings, particularly 

 in the underlying mica schist. All of the rocks present, including 

 the pegmatite, contain some pyrite, and here as elsewhere the ore 

 body is merely that part of the gneiss and schist formation in which 

 the amount of pyrite is particularly large. 



The pyrite is very irregularly distributed, appearing in streaks, 

 hunches and veins (figure i).^ As the mineral increases in 

 amount these irregular masses blend and form large and rich ore 

 l)odies, in which the relation -of the pyrite to the rock is wholly 

 obscured. But in the leaner ore the pyrite appears distinctly, so far 

 as its present distribution is concerned, to be of vein origin for, 

 while commonly running parallel to the banding of the rocks, it 



^ For all the photographs in this paper the writer is imltiUti^d to the kind- 

 Mess and skill of Professor Gilbert van Ingen/ 



