TOPOGRAPHY.
Attention is given here rather to the details than the general aspect of the country. It exhibits the usual monotonous succession of low rocky hills and lake-containing depressions, the even horizon seen from the summit of any large hill, being only rarely notched by a prominence of unusual height. In the spring of 1908 virtually the whole area was forested, but during September the extreme dryness of the country and the unusually large number of camping parties combined to cause bush fires over much of the country between the East and West branches. The vegetable loam has been removed from extensive tracts leaving the rock formations exposed, but the charred tree trunks have fallen so as to cover the burnt districts with a ‘slash,’ which greatly impedes cross-country travel, so that what has been gained in one respect is more than counterbalanced in another. Especially is this the case in the country west of Gowganda and Obushkong lakes, and near the Forks.
The general surface may be characterized as of comparatively low-relief, the hills not often rising over 200 feet, but here and there over the country are conspicuous elevations, visible at long distances, which form useful landmarks and from whose summits comprehensive birds-eye impressions of the surrounding country are possible. Structurally they appear to be, in a few cases, resistant knobs of Keewatin, which project well above the general peneplain level, but more commonly they are tilted ridges of Huronian. A characteristic representative of the latter type forms a long ridge beginning a mile and a quarter north-east of Duncan lake and extending thence for several miles in a north-easterly direction. The south-east side of this ridge slopes gently at an angle corresponding with the dip of the beds, but the north-west face is an abrupt cliff dropping almost perpendicularly for about 400 feet to a flat sandy plain which extends westward and northward for several miles, beyond which are other monadnock-like knobs. The accompanying diagram is intended to represent the structure in vertical cross-section.
Fig. 2.—Vertical section across Huron Ridge, North of Duncan Lake.
Another ridge of similar character, standing 550 feet above the level of Duncan lake, is visible from the ridge just described and from points on Duncan and Otto lakes, and adjoining country. Its position as indicated on the map is about four miles north of the large island in the middle of Duncan lake, a view of it from this point being shown in [fig. 4]. In this case the east face is perpendicular. A prominent hill of the same kind is visible from Obushkong lake, lying a short distance to the north-west of that body. Just west of Mosher lake as represented in [fig. 5], two round hills of about equal size rise 300 feet above the water level. The more southerly of the two is of Keewatin, while that to the north is composed wholly of diabase, Huronian lying around the base of each. Bold, but less individualized elevations are common in the neighbourhood of Kenisheong lake, and other localities. All these hills are markedly rocky and free from soil.
Less conspicuous than these great masses are certain minor, but persistent features which are directly referable to geological conditions. Within Huronian areas there is a distinct tendency toward the development of a system of parallel ridges similar in structure and mode of origin to the hill at the north-east of Duncan lake. This feature is developed with special regularity in the southern part of the wedge between Duncan lake and the West branch, where a succession of north and south ridges alternate with strips of swampy ground. The western faces of the ridge are bare and cliff-like, while the eastern slopes are gentle, well soil-covered and forested.
The post-Huronian diabase is an equally potent topographical factor. Its surface is one of marked irregularity, but the peculiarly distinctive features occur at its contacts with the Huronian. These contacts appear to be zones of low erosive resistance, and are commonly coincident with ravines, walled on one side by diabase, on the other by Huronian. Small lakes may occur at intervals along them as, for example, between Firth lake and the West branch. This erosion feature is well shown by the configuration of Gowganda lake, where diabase bodies are unusually abundant; both of the long arms to the north-west lie in trough-like depressions marking the edges of the eastern diabase mass. The same tendency in an incipient condition is observable on the east side of the large peninsula where a series of three land-locked bays extend along the contact between the eastern diabase mass and the Huronian. Near the middle of Duncan lake, a diabase-Huronian contact which crosses the lake diagonally is marked by two deep bays, one extending to the north, the other southward. While this tendency is an evident one it is not to be understood as invariable; the large island in Duncan lake between the two above-mentioned bays is sufficient to indicate that contacts may lie in high ground, yet even here there are minor features indicating the contact zone to be structurally weak.
Another less explicable topographic peculiarity becomes apparent only upon scrutiny of the drainage system. A brief consideration of the map shows that both East and West branches follow peculiar zig-zag courses running north for a short distance, then turning abruptly east, this feature recurring repeatedly. In some instances the east-west portion of both branches lies in the same line. In the case of Zigzag lake and adjacent portions of the West branch this feature is repeated with an almost conventional regularity, which precludes attributing it to chance causes. Many of the smaller lakes—Foot lake, for instance—exhibit the same character on a small scale. This abnormality has been commented upon by investigators in the country to the east, the courses there, however, being N.E.-S.W. and N.W.-S.E. Regional faulting is suggested in explanation. The canyon-like east and west walls of Zigzag lake suggest such conditions, but a discussion of the matter must be deferred until further data can be collected.