The rocks belonging to the third division, as before stated, grade into the division above them, and the line between them cannot be drawn sharply.
The typical rock of the division is fine-grained and very siliceous, with minute particles of silica coated with red oxide of iron, forming a coarse impure red jasper.
These jasper rocks usually occur in thin broken bands, the partings between them being filled with a finely-divided mixture of hematite, magnetite and jasper. The hematite is greatly in excess of the magnetite. The association of the iron ores and the jasper is intimate, and they must have been deposited simultaneously from aqueous solutions probably leached from the cherty carbonate measures above. Microscopic sections from these rocks are almost identical with those of jaspilite figured by Van Hise in his monograph on the iron-bearing rocks of the Lake Superior region; and they must have had the same origin that he has assigned to these rocks, namely, enrichments deposited by water subsequent to the formation of the bedded rocks in which they are found as partings, and filling the most minute cavities.
The amount of ore in this admixture of hematite and jasper varies greatly. Where the ore is poor, the jaspery rock predominates and incloses lenses of hematite, while where the hematite is most plentiful it incloses similar lenses of jasper. The detailed description of these rocks shows that the measures of this division contain an immense amount of hematite. The rocks of the division do not occur on all the islands, being wanting on Flint, Belanger and Ross. On Anderson they are represented by a few thin beds not rich in ore, while on Clarke they form the summit of the section with a thickness of eighty feet. They reach their maximum development on Gillies and Taylor, where their ores are richest and most concentrated. Farther northward they become thinner and poorer in ore, being twenty feet thick on Davieau and only eight feet thick on McTavish, where they die out. No trace of these measures is found underlying the upper rocks on the islands south of the Nastapoka group.
The fourth division, consisting of red jaspilites, is an arbitrary one, of use only as a subdivision of the iron-bearing rocks. Wherever the jaspilites are well developed the richer beds are underlain with leaner measures, unfit for working, and these poorer ores constitute this division. On Clarke island these beds are twenty feet thick; on Gillies they vary from ten to twenty feet in thickness, on Taylor they are ten feet, while to the northward they merge into the overlying division, all poor in iron ores.
The richest ores are found in division III, where extensive beds several feet in thickness are found containing ore practically free from jasper, and ranging in iron values from thirty per cent to sixty per cent. Most of these ores, however, would require separation from the bands and lenses of jasper before becoming sufficiently rich to be economically treated in the furnace. The position of the ores on the islands separated from the mainland by a sound varying from a mile to four miles in width, with excellent, almost tideless, harbours, constitute ideal conditions for shipment. The mining of the ores would also be easy and cheap, if advantage were taken of the great waterpower of the Nastapoka river, which falls 160 feet into the sea within a few miles of the best ore deposits, and from which electrical power might be generated easily and cheaply. Owing to the distance of these ores from the nearest furnaces, and the want of experience in the navigation of Hudson strait, the shipment of them is at present out of the question. No coal is found in Hudson bay, so that economical smelting near the mines cannot be attempted, until electrical smelting becomes practicable some time in the future.
In all the fields where extensive areas of iron-bearing rocks occur in the Lake Superior region, the search by drilling has disclosed large deposits of concentrated ore, and there is little doubt that such a search in the Hudson bay region would lead to similar discoveries, as the manner in which the ores occur is favourable for such concentrations.
Mica.—Active mining operations for mica are being carried on at Lake harbour, on the north side of Hudson strait. This mine is being worked in connection with the whaling steamer Active. A number of white men are brought to the place from Scotland in the early summer, who, with the assistance of the Eskimos, work the mine, and then return home in the fall. Last summer thirteen tons of excellent mica were taken out in this manner. Other deposits of this mineral will probably be found on that coast to the westward in association with the crystalline limestones so largely developed there. A mica mine was opened some years ago on the west side of Cumberland gulf, but for some reason was shortly after abandoned.
Graphite.—Extensive bands, or veins, of this mineral were discovered by Mr. Caldwell to the south of Port Burwell along the east shore of Ungava bay. Graphite has also been found in the neighbourhood of Cape Wolstenholme, and along the east side of Baffin island, but no attempt has been made to develop any of the outcrops.
Molybdenite.—Flattened crystals of molybdenite have been found in many localities in the pegmatite veins penetrating the Laurentian rocks, but in no place has the quantity been sufficient for mining.