Wild animals are not abundant, and will probably become less so as the country is occupied by prospecting and mining camps. Moose were plentiful in 1908 and some black bears were seen. As a source of food the abundance of pickerel and pike is of much greater importance. Brook trout do not occur in the Montreal River waters, but are caught farther to the west and north.
GENERAL GEOLOGY.
OUTLINE OF GEOLOGICAL HISTORY.
Though the geology of the region presents considerable complexity of detail, the general historical facts are distinct and go to show that the whole complex of formations and systems is capable of separation into four major divisions widely different from one another. The mutual relationships of these divisions, a knowledge of which is essential to a thorough comprehension of the geology, are succinctly expressed by the accompanying diagram.
Fig. 3.—Diagram illustrating geological relationships of Montreal River district.
The oldest division, the Keewatin, comprises a complex association of metamorphosed rocks, principally eruptive, characterized by well-developed, secondary schistosity and prevalently dark colours. They dip at angles approaching 90° and range in texture from soft, fissile, chorite schists to fine-grained gneisses or altered diabases. In the Montreal River district the Keewatin areas are not entirely visible, being overlain by other rocks, but they are thought to represent the bottoms of trough-like folds, produced by the upward intrusion of igneous matter which now constitutes the Laurentian. The latter forms the second division, its origin being apparent from the foregoing statement. It is wholly igneous, consisting of granite and allied coarsely crystalline rocks essentially pale-coloured owing to their richness in quartz and feldspars. Gneissic structure has been developed in varying degrees, so that all gradations between granite and gneisses exist; but it never attains the perfection found in the Keewatin. Near their contacts with the Keewatin, the gneisses are apt to contain dark bands and ribbons of the latter so highly crystalline as to conceal their identity.
Wherever visible the surface of the Keewatin and Laurentian presents an irregular, deeply worn appearance, the result of extremely protracted exposure to erosive agencies. To the best of geological knowledge the same conditions hold where they lie buried under the Huronian, indicating that a great period of denudation separates the latter from the Archæan. The combined Keewatin and Laurentian, or Archæan system, is therefore to be conceived as forming at all points in the district an ancient denuded foundation or floor upon which rests the much younger Huronian system.
This third division is, in the Montreal River district, wholly sedimentary and easily distinguished from the other rocks by its bedded structure and clastic nature. As it is the only sedimentary system represented, its members are not easily confused with any other, especially as their original structure is not obscured by metamorphic alteration. Locally this is not strictly true; in the vicinity of diabase intrusions they have been hardened and shattered so as to simulate the Keewatin, but the zones of alteration are narrow and readily identified by their gradation into adjacent areas of less altered types. At present the Huronian forms a discontinuous rock mantle over the Archæan, formerly more complete, but now worn through in places so as to expose portions of the crystalline basement.
The fourth division includes all eruptives known to be younger than the Huronian. Owing to the discontinuity of the latter it is not always easy to decide what rocks should be included in this group, for in some cases rather fresh-looking eruptives occur in the Keewatin which probably would also intrude the Huronian were it present; lacking the necessary information their chronological position can be only loosely fixed. By far the most extensive and important of the post-Huronian eruptives is the diabase with which the silver deposits are associated. This penetrates both Archæan and Huronian, but is ordinarily distinguishable by its unusual freshness, dark colour, and crystalline appearance. In certain cases, to be described subsequently, it may be confused with certain other diabases. Magmatic differentiative processes have evolved diabase types of very dissimilar appearance and mineralogical composition, of which a pink aplite occurring in dike form is the most extreme. Olivine diabase dikes are also present in the region, but in far less abundance.