It seems tolerably certain that Logan included in his Huronian two series of rocks of quite different ages, the Huronian of lake Huron being probably much younger than the rocks so named on lake Superior. This conclusion is in agreement with Lawson's view, in accordance with which he gave the name Keewatin to the Lake of the Woods schist, 50 and compared them with the Doré rocks, distinguishing the latter from the original Huronian. On the Shores of Heron Bay. Schists of Heron Bay. Another large area of schists mapped by Bell as Huronian, but not described by Logan, occurs 35 miles to the northwest around Heron bay, where the Canadian Pacific railway first touches lake Superior. Two days were devoted to a study of these rocks on the shores of the bay and along the railway to the west between Huron bay and Peninsula. 51 These rocks are first met at the point turning northward from Pic river to Heron bay, where they consist of green schist and felsite schist with variable strike and dip, probably from the influence of the adjoining eruptive gneiss or granite which sends dikes into them. Rounding the point one finds schist conglomerate with a strike of 110° to 120° and a nearly vertical dip. These rocks are greatly sheared, so that the forms of the pebbles are almost indistinguishable except where lapped by the waves. A little way off they look very gneissoid. The conglomerate contains pebbles and boulders of all sizes up to blocks two feet long, mainly reddish or yellow granite or quartz diorite or porphyry, and green and dark gray basic rocks and schists. The matrix is generally dark green and more easily weathered than the boulders. In most cases the pebbles are considerably rolled out, and in parts they show only as bands of slightly varying color, or turn to felsite schists in which no pebble can be seen. The strike and dip vary greatly, the former from 60° to 120° with an average of about east and west; and the latter from 40° or in 50 Geol. Sur. Can., 1885, cc. 61 Geol. Sur. Can., 1870-71, p. 328. Bell mentions "slate conglomerate" with dark green trap as the rocks east of the mouth of Pic river, but does not describe them. one place 30° to the north to verticality. The breadth across the strike is about four miles, from the point turning towards the mouth of the Pic to the railway station; and the distance followed along the strike is about 2 miles. Going towards Peninsula the schist conglomerate is followed by green-gray, very fissile slate or phyllite, then a band of felsite schist with faint traces of flattened pebbles, then a band of dark gray slaty rock, a series of hard green agglomerates and near the Peninsula gravel pit by a large eruptive area. All the schistose rocks have dips running from 45° to the north to vertical. They are however a good deal disturbed by dikes of both acid and basic rocks. Whether the slates are lower or higher in the scale than the schist conglomerate was not settled. The unusual width of the conglomerate beds is worthy of remark. It may result however from close folding and not represent a continuous sequence of beds. The schistosity conforms in general to the bedding as shown by the bands of more numerous and less numerous pebbles. The rocks just described conform to the Keewatin rather than the typical Huronian type. Impressions as to the true Sequence of Archæan Formations. The general impression left by our summer's work in the region is that Logan has included two series of rocks of very different ages in his Huronian; that the series on lake Huron, the most carefully studied and the only one mapped in detail, is of later age than the Doré rocks and probably also than the western Keewatin (or Ontarian); and that in the typical Huronian region the Keewatin is probably represented by the bands and fragments of green and gray schists enclosed in the Laurentian gneiss and granite. If these impressions are correct the true succession in time is Keewatin, Laurentian, Huronian; the term Laurentian being confined to the areas of granite and granitoid gneiss corresponding to the Ottawa gneiss of eastern Canada, and having eruptive relations with the Keewatin. The suggestion just made implies an immense lapse of time between the Keewatin and also the Laurentian and the overlying Huronian. The gap between the Keewatin and the Huronian was long enough to permit of the Laurentian gneiss erupting through the Keewatin rocks, and throwing them into closely folded synclines; after which the granite and gneiss consolidated at great depths and the whole mountainous region was carved down to a peneplain. On this the basal conglomerate, of the typical Huronian was deposited. The basal complex recognized everywhere as underlying the ordinary sedimentary rocks is considered by us to consist of two very distinct groups of rocks of quite different ages, the older one mainly of basic green schists but including also immense beds of schist conglomerate, the later one consisting mainly of moderately acid eruptives. Character Series. The Keweenawan Series. In the field covered by last summer's work the Keweenawan, Logan's Upper Copperbearing series, includes many basic istics of the eruptives such as diabase and amygdaloids, some acid eruptives such as quartz porphyry, quartzless porphyry and felsite, and also sedimentary rocks such as sandstone, shale and conglomerate; in fact, most of the rocks described by Irving as occurring in the Keweenawan of the United States. 52 One variety of conglomerate, basal and made up chiefly of the underlying Laurentian rocks, has apparently not been found south or west of lake Superior, though not uncommon on the northeast shore. As a very full list of authorities on these rocks is given by Irving it will be unnecessary to refer to them in detail here. The northeast shore Keweenawan has been described more or less fully by Logan, 53 Dawson and Macfarlane and needs no lengthy account. Following up the shore from Sault Ste. Marie, rocks of this age are first seen at Gros Copper Bearing Rocks of L. Sup., U. S. Geol. Sur., 1883. 53 Geol. Can., p. 67, etc., Logan ; Can. Nat. and Geol., vol. II., 1857, p. 1-12, Dawson; Geol. Sur. Can., 1866, 115-143; Can. Nat. and Geol., 1866-8 (2), vol. II., pp. 177-202 and 241-257; and also 1879 (2), vol. IX., pp. 91-102, Macfarlane. the point a patch of typical amygdaloid rests against the foot of the Laurentian mass; and the same rock occurs at three points on the east side of Batchawana bay. The area at the northeast of this bay seems to be considerable, a range of hills of amygdaloid running east and west for some distance. At one point a small patch of green amygdaloid is seen to form a breccia, ramifying among the granite blocks at the point of con tact. Next comes the large area of Mamainse, so fully described by various writers because of the copper mines located upon it. Amygdaloids occur once more on the north side of Pointe aux Mines, and connected with them a basal conglomerate or breccia containing large boulders of gneiss or granite forming the bottom of the series. Beyond this for some distance no large stretches of Keweenawan are found, but that these rocks once occupied the region and probably still exist beneath the lake is shown by occasional patches of the basal conglomerate filling old chasins of the Laurentian. As their greenish cement is soft, the conglomerates are more readily acted on by waves than the Laurentian rocks around, and the Keeweenawan shore line is being restored by the waters of the lake, the ancient boulders being set once more rolling after their long rest. To the south of Gargantua there are curious red shaly rocks with numerous cavities almost like amygdaloidal openings, and at the extremity of the cape amygdaloids resting directly on gneiss without the usual basal conglomerate. Beyond this, undoubted Keweenawan rocks were found only at two points, between Pilot harbor and Pucaswa, nearly north of Michipicoton island; and at Swallow river about 15 miles northwest; in both cases remnants of basal conglomerate preserved by having been deposited between Laurentian walls in narrow ravines. Each of them shows a brownish-purple ground mass more or less crowded with granite and less often diabase pebbles. It is probable that many of the very numerous diabase dikes to be found all along this shore are really of Keweenawan age, |