ARTICLE IX.-Notes on the Geology of Murray Bay-Lower St. Lawrence. By J. W. DAWSON, LL.D., F.G.S. (Read before the Natural History Society.) Murray or Mal Bay on the north side of the River St. Lawrence, and about 90 miles below Quebec, is well known as a place of resort to summer tourists and sea bathers, and has not been unvisited by geologists. In 1822, Dr. Bigsby, one of the earliest explorers of Canadian geology, and still in his green old age a prominent member of the Geological Society of London, spent a few days at this place, and published a most interesting and graphic account of its topography and geology, in Silliman's American Journal. In 1831, Capt. Baddely published in the Transactions of the Literary and Historical Society of Quebec, an account of the neighbouring Bay of St. Paul, with a notice of the earthquakes which appear to visit this district more frequently than any other part of Canada. In 1849 the steps of our Provincial geologist were directed thither, in consequence of a fabulous report of the discovery of coal at Bay St. Paul; and a short but clear and accurate account of the structure of this part of Canada appeared in the Report of the Survey for that year. Learning from these previous observers, that the locality is of much geological interest, I determined in visiting it for a few days in the past summer, to pick up such gleanings as my prede * Vol. 5, 1822. † Quebec Transactions, vol. II. See also paper by the author on the earthquake of 1860. Can. Nat., vol. 5. cessors might have left, and in this I was greatly aided by one of my students, Mr. R. Ramsay of Montreal, who happened to be spending his vacation there. The features of the place have been admirably described by Dr. Bigsby and Sir W. E. Logan, so that a very few remarks on this subject may suffice here. In approaching the bay from the west, the voyager passes along the base of lofty cliffs crowned by forests and broken by a few wooded ravines, down which little brooks dash to the shore. Near the termination of this wall of cliffs, and at the base of a steep ascent leading to a gap separating the last outlier of rock from the main mass, stands the steamboat pier. Ascending the rising ground above the pier, and passing to its northern side, one sees in the foreground a row of cottages extending along the western side of the bay, whose waters at high tide rise close to the low bank, and when they recede leave an immense flat of sand and boulders, across which stretch the long brush weirs of the fishermen. Beyond are seen the sides of the bay rising into terraced hills and converging toward the mouth of the Murray Bay River, where concealed by trees are the church and village of Mal Bay; and still farther the eye can trace the deep valley of the river winding among high wooded hills, that rise one over another in the blue distance. It is a beautiful spot, well worthy of taking a leading place among the summer resting places of our worn and wearied citizens. The general geology of Murray Bay may be thus sketched. The higher hills consist of rocks of the Laurentian System, the oldest strata known to geologists; and in some places as at the high cliffs before mentioned, and at Cape Heu on the opposite side of the bay, these come boldly down to the shore. In other places the coast cliffs and reefs are Lower Silurian, and abound in marine fossils, and these beds in some places mantle the hills to a considerable height, and run a long way up the valley of the river. The terraces of sand and gravel along the sides of the bay, and the deep clay of the river valley, are of Post Pliocene date, and contain shells identical in species with those now living in the Gulf of St. Lawrence. I shall notice these formatione in their order. 1. Laurentian System. These venerable rocks, ancient above all others, are admirably exposed in the coast cliffs above mentioned, and in several other places in the vicinity of the bay, but they present a strange and puzzling aspect to the observer. Proved by the investigations of Logan and Hunt, to have once been sedimentary rocks, they have been so changed by heat and chemical action, that they retain no resemblance to the sands, clays, and limestones, of which they were originally composed. They now appear as beautifully crystalline layers, which have when in a yielding and flexible condition, been bent and crumpled as if for long ages they had been kneaded by the hands of Titans, so that it is difficult to form any conception either of their original nature or arrangement. The greater number of rocks are eloquent to the geologist of the history of life in past periods of the earth, but these Laurentian beds preserve an obstinate silence, only hinting in their flakes of graphite and their crystalline limestones, that they have a story which they cannot be persuaded to tell. Still they afford very instructive examples of the changes which may be effected by metamorphism in aqueous sediments, and they abound in interesting and curious crystallized minerals. In the high cliff commencing immediately west of the pier, they are well exposed; and at this place the or der of succession is as follows, apparently in ascending order, though these beds are here so often inverted that little reliance can be placed on apparent superposition. 1. Gneiss of various colours and qualities, with both lime and potash felspars, and containing beds of mica slate, with large nodules of garnet, around which the beds bend as if the garnets had originally been foreign masses or pebbles. or pebbles. In some places these beds hold bands or dykes of a coarse-grained red felspar. These gneissose beds are of great thickness and occupy the greater part of this long range of cliffs. They reappear on the opposite side, at and beyond Cape Heu. 2. White quartz rock, perfectly compact, with thin bands of hornblendic and micaceous schist, and in the upper part with some crystals of flesh-coloured felspar. This bed or a similar one appears on the opposite side of the bay on both sides of Cape Heu, where in one place it immediately underlies the Silurian beds, as has been observed by Sir W. E. Logan, but it is clearly a member of the Laurentian series. 3. Impure crystalline dolomite, and light-coloured laminated serpentine. These are only a few feet in thickness, and in some places seem reduced to a few inches. Being the softest part of these rocks, they form a depression in the cliff or reef, and are often hidden by gravel or rubbish. 4. Gneiss as before. 5. Black hornblendic slate with films of mica on the planes of cleavage or bedding. On the opposite side of the bay the gneiss rises into the high and rugged promontory of Cape Heu, in which a great thickness of this rock is exposed, presenting a succession of hard angular ridges, and having its strike nearly in the direction of the shore or S. 25° W. (see Fig. 1). Cape Heu rises through Silurian limestones which appear on both sides of it and inland. On the west side after an interval occupied by the Silurian beds, the gneiss reappears with a high dip to the N. W., and containing thick veins of red felspar. In tracing it along the shore it becomes nearly horizontal, and then dips to the north, and finally becomes vertical and much contorted. Here it contains a vein or bed of coarse grained granite. Next appear mica and hornblende slates, the former with garnets and having a strike S. 20° W. to S. 30° W: then after a space of 150 yards without section, white quartz rock 45 feet thick, and in a vertical position, and succeeding this gneiss with bands apparently of crystalline limestone 4 feet, coarse crystalline dolomite and serpentine 10 feet, and gneiss 4 feet; after which these rocks are concealed by the Silurian beds, resting on them unconformably. Westward of Cape Heu the quartz rock again appears, and seems here to overlie the gneiss, and no other beds appear between it and the Silurian rocks, which here appear in great mass, forming the conspicuous cliff of L'Ecorché. West of this, and toward Cape Baleine, the shore runs nearly in the junction of the Laurentian and Silurian, the alternate appearance of which at the several points and capes, gives a confused appearance to the coast section, increased by the fact that the Silurian beds are bent into an anticlinal fold near the junction, and that dislocation and denudation have moulded the Laurentian into such irregular forms. Fig. 2 represents a portion of the shore looking east. The Silurian rocks are shaded and appear in the foreground, in a reef dry at low water, and in the cliff of L'Ecorché. The Lauren tian forms irregular masses in the middle ground, and Cape Heu presents its bold front in the distance. 2. Silurian System. These rocks rest unconformably on the old gnarled Laurentian beds, and are here sandy in the lower part, simulating the appearance of the Potsdam sandstone, seen in a similar position further west. A little higher they assume the aspect of Calcareous sandstones, and these are overlaid by limestones capped by dark calcareous shales. We thus have a series which at first sight might be supposed to be a miniature representation of the whole lower Silurian of Canada, from the Potsdam sandstone to the Utica slate. According to Mr. Billings, however, the fossils of these beds belong to the middle part of this series, between the Chazy limestone and Trenton limestone, so that here the older members of the Lower Silurian series either do not occur or are represented only by a few feet of sandstone, nearly destitute of fossils. This corresponds with a conclusion arrived at by Sir William Logan, as the result of very extensive observation, that in the early part of the Silurian period, the old Laurentian shore running along the north of Canada was sinking beneath the sea, which was gradually carrying the newer deposits further and further up its sides, so that the older beds are often concealed from view. The subsidence must have been greater in some places than in others, or the upper deposits have in some places been more removed by subsequent denudation, for while in the middle of Canada near the confluence of the Ottawa, the series is complete, both to the westward and eastward the older members of the Silurian series are concealed. I was much struck with this lately at Madoc in Upper Canada, where the junction of hard slaty rocks of the Laurentian series with a Lower Silurian limestone is well seen. latter under the limestone presents a shattered and weathered surface that must have long endured the action of the elements. while the limestone, a mass of fragments of shells and corals, contains irregular fragments of the older rock, and has filled up the crevices of the latter with whole and broken Orthoceratites, and other shells, which lie just as the wave threw them in. It requires scarcely any imagination in such a place to fancy one's self standing on the old Laurentian shore, and watching the bright billows hurling their load of shells and fragments against the shore, and year by year reaching higher and higher on the land, The |