NATURAL HISTORY SOCIETY OF MONTREAL [Incorporated 1832.] OFFICERS-SESSION 1899-1900. Patron: HIS EXCELLENCY THE GOVERNOR-GENERAL OF CANADA. SIR J. WILLIAM DAWSON, LL.D., F. R.S., F. R.S.C. Editing and Exchange Committee: REV. ROBT. CAMPBELL, M.A., D.D., Chairman. FRANK D. ADAMS, Ph.D., F. R.S.C. A. T. DRUMMOND, LL.D., Kingston, Ont. H. H. LYMAN, M. A. PROF. E. W. MCBRIDE, M. A., B.Sc. J. F. WHITEAVES, Ottawa, Ont. THE JAN 25 1900 CAMBRIDGE, MASS. CANADIAN RECORD OF SCIENCE. VOL. VIII. JULY, 1899. No. 2. STUDIES IN THE GEOLOGY OF THE VICINITY OF MONTREAL WHICH MIGHT BE UNDERTAKEN BY MEMBERS OF THE NATURAL HISTORY SOCIETY. BY PROF. FRANK D. ADAMS, PH.D. Although much has been done towards working out the geology of the vicinity of Montreal, still more remains to be done before our knowledge of the subject is at all complete. The geological relations, which are in the main simple, nevertheless present such a mass of detail that much time and patient work on the part of many observers will be required before we shall understand fully the structure and the past history of our Island. Much of this work is of such a character that it can be easily carried out by members of the Natural History Society, and it is in the hope of enlisting some of our members in the work that it is proposed in the present paper to point out very briefly some of the chief lines of investigation which present themselves. The district about the city is underlain chiefly by nearly horizontal strata of Lower Silurian age. These in many places where they are well exposed, contain an abundance of fossil remains; in fact the limestone strata are entirely of organic origin. Each of the several formations presents its special fauna, composed of creatures all of which have been long extinct, and which are therefore, for the most part very different from the forms of life now inhabiting our globe. Before a thorough knowledge of each of these several faunas can be obtained and their relations to one another satisfactorily established, large collections of fossils must be made from the several formations, so that we may have as nearly as possible all the forms which are present in these successive oceanic deposits. For these purposes complete collections should be made of all the fossils to be found in the various quarries about the city, as, for instance, the Mile End quarries, and those at Pointe Claire and St. Martin's Junction. In this connection the small occurrences of limestone at the water edge on the south side of St. Helen's Island are of especial interest, as being very much more recent than any of the other limestones in this part of the Province, and a thorough knowledge of these fossils is for this and for many other reasons of the greatest interest. The principal fossils occurring in the quarries about the city are figured and described in the Geology of Canada, published by the Geological Survey of Canada in 1863, a copy of which is to be found in the library of the Society, while lists of the fossils found up to the present time in St. Helen's Island rocks are given by Mr. Donald and Dr. Deeks in two papers which have already appeared in the CANADIAN RECORD OF SCIENCE. For those members of the Society particularly interested in the aucient volcanic phenomena displayed in the vicinity of Montreal, Mount Royal affords abundant opportunity for work and study. The "Mountain," as is well known, is the root or remnant of an old volcano, wasted and worn down through successive long geological ages, by the continuous action of rain, frost and the other agents of decay. The piles of volcanic ashes, the crater, the lava streams and other superficial features have long since disappeared; only the hard basal portion of the mountain has survived; even now it is year by year falling to pieces, as can be seen at the foot of all the steep slopes on the mountain side, notably that opposite the head of McTavish Street. There were, speaking generally, three stages in the history of the activity of the mountain, marked by the outpouring of three different classes of rock. Each of these can still be recognized and studied, and much remains to be learned concerning them. At the first eruption a dark-coloured basic rock was poured out, represented by the main body of Mount Royal, as seen in all the cuttings on the upper part of the mountain and in the cemeteries. This is a rock found in but few other places in the world, and known as Theralite or Essexite. On looking at a fresh fracture it is seen to be composed of constituents, some of which are colourless and some of which are black. The colourless ones are feldspar and nepheline, the black ones pyroxene and hornblende. The relative proportion of these minerals varies from place to place, in that part of the mountain occupied by this rock, the rock being in some places dull gray in colour, but in others black. It often shows a distinct flow structure which it acquired when moving up through the throat of the volcano while still in a semi-fluid condition. After the rock of this first eruption had cooled, becoming hard and solid, it was rent asunder and shattered, undoubtedly with the accompaniment of violent earthquakes. On a line which runs along the back of the mountain and up through this shattered zone there came a second eruption, of rock of a different character. This is much lighter in colour, a pale gray, and is seen excellently exposed in the great quarry worked by the Corporation for road material at the back of the mountain at Outremont. This rock is a nepheline syenite, and contains so much nepheline that if a little of it be finely powdered and boiled with acid for a few minutes it will pass into a mass of thick jelly. The final outburst of volcanic energy on the part of Mount Royal is represented by the swarm of narrow dykes or walls of igneous rock which cut not only through the limestones of the region but also through the rocks of both of the former eruptions just referred to. These, although erupted during the final stage, are not all absolutely identical in age; in fact, in the excavation made for the reservoir on Peel Street some seven distinct sets of dykes, each cutting across, and therefore more recent than the previous ones, could be seen. These dykes are composed of a variety of rocks; all of them are very rare and found in but few other places in the world. Now, although detailed study of these rocks requires some special knowledge of the methods of modern petrography, no study of the region can be made until the necessary materials for it have been collected. The collection of such materials, in itself an occupation by no means devoid of interest, might easily be undertaken by members of the Society, and the collections, if carefully labelled and deposited in the Society's Museum, would always be available for detailed study. Such a detailed study is now being undertaken by Dr. Harrington and the writer, who would be glad to examine and describe any carefully collected material. It is from the dykes of the third eruption that collections of the greatest value can be made, especially where these are exposed from time to time in cuttings and excavations which are subsequently filled in again, and the exposures thus rendered inaccessible. In collecting specimens from such dykes, the width of the dyke, measured across it, that is, at right angles to its dip, if it be not vertical, should be noted, as also the direction in which |