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Professor Gustavus Rose, to whom I submitted specimens of this dike, found it to be dolerite, and composed of greenish black augite and Labrador feldspar, the latter being the most abundant ingredient. A small quantity of magnetic iron, perhaps titaniferous, is also present.
Both these rocks are composed of triclinic feldspar and augite with more or less olivine, magnetic or titaniferous oxide of iron, and usually a little nepheline, leucite, and apatite; basalt usually contains considerably more olivine than melaphyre, but chemically they are closely allied, although the melaphyres usually contain more silica and alumina, with less oxides of iron, lime, and magnesia, than the basalts.
The result of this analysis is interesting, because both the ancient and modern lavas of Etna consist in like manner of augite, Labradorite, and titaniferous iron. An interesting discovery was made in 1867 by Mr. E.A. Wunsch in the carboniferous strata of the north-eastern part of the island of Arran.
But the distance from Quebec was too great for profitable transportation and, although Père Dablon in 1670 sent down an accurate description of the great masses of ore in the Lake Superior region, many generations were to pass before any serious attempt could be made to develop this source of wealth. Nearer at hand some titaniferous iron ore was discovered, at Baie St.
Some fragments of titaniferous iron ore, with haematite changed by heat, and magnetic, lay in the gully, which had worn itself a channel on the north side of the village. The Bua, like most African streams whose sources I have seen, rises in an oozing boggy spot. Another stream, the Tembwé, rises near the same spot, and flows N.W. into, the Loangwa. We saw Shuaré palms in its bed.
The formation is upper Silurian or lower Devonian, a transition to gneiss, but not highly metamorphic. No fossils have yet been found: if any exist they would be microscopic. Where talcose it is bluish, and shows streaks of 'black sand, titaniferous iron. The grey sand washes to white. There are pot-holes which have been filled with either a pudding or a breccia of quartz.
The basaltic rocks are of a black colour and thinly stratified; they are generally highly vesicular, but occasionally compact; some of them contain numerous crystals of glassy feldspar and octahedrons of titaniferous iron; others abound with crystals of augite and grains of olivine.
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