Price Five Shillingfs. TRANSACTIONS ^bintergl ^wfcgial ^0aetj. VOL. III. PART I. EDINBUEGH: ^rinlib for iht %atui\i^ BY NEIT^L AND COMPANY. 1877. Registered in terms of the Act 5 and 6 Vict. cap. 45. All rights reserved to the Edinburgh Geological Society vndT the in-oi-isions of the said Act. LIST OF OFFICE-BEARERS OK THE EDINBURGH GEOLOGICAL SOCIETY FOE SESSION 1876-77, BEING THE FORTY-THIRD. ^Satron. His Grace the Duke hf Akgyll, K.T., D.C'.L., F.R.S. {President. David Milne-Home of Wedderburn and Milnegraden, LL.D., C'.R.S.E., F.G.S., Chairman of Council of the Meteorological Society of Scotland. 'F(ce=13rfsiBcnts. .LiiiES Brtce, M.A., LL.D., r-.R.S.E., F.G.S. •Tames Mei.\tn', Bonnington, President of the Scottish Chamber of Agriculture. Ilonorarp 5ccrctarn. Halph Richardson, W.S., F.R.S.E., 35 Castle Street, Edinburgh; and Newpark House, Midcalder. STrfasurcr. George Lyon, George Heriot's Hospital Chambers, 7 Royal E.\change, Edinburgh. librarian. Curator of JHustum. R. D. Keb. John Henderson. I ffiouncdiora. Andrew Fleming, M.D., C'.R.S.E., Dejmty Surgeon-General H.M.I. A. John Buchanan, C.E. I Alexander Somervail. Andrew Taylor, F.C.S., Mineral Surveyor, Etlinburgh. James Linn, of H.M. Geological Survey of Scotland. Thomas W. Kilgocr, Royal Bank of Scotland. STANDING COMMITTEES. IZibrarp Committee The President, Librarian, Honorary Secretary, Treasurer, and Messrs James M'Intosh, Bookseller, and James Mklvin. jfJtuscum Commhtfc. The President, Curator, Honorary Secretary, Treasurer, and Dr W. T. Black, Surgeon-Major, and Ale.xander Somervail. ^9ublt8f)ing CTommftuc. The President, Honorary Secretary, Treasurer, .ind Messrs John Henderson, Duncan Maclachlan, Publisher, and Andrew Taylor. 1Coti)(ans ants jPifc ^Pali'ontological Committer. Alexander Somervail, Convener; Dr .James Bryce, and Messrs John Henderson and James Linn, and the Honorary Secretary, and Treasurer. ISlutiitors. Roderick A. F. A. Coyne, C.E., and Thomas W. Kilcour. Society's Library, Museum, and Rooms, No. 5 St Andrew Square, Edinburgh. Assistant Libi-arian and Officey—'Mr Dawso:». All Ci' iiimunicalions and Donations to be addressed to the Honorary Secretary, .35 Castle Street, Edinburgh. — TRANSACTIONS OF THE EDINBURGH GEOLOGICAL SOCIETY. SESSIONS 1874-7 r. Thursday, 5th November 1874. The Society held its Forty-First Anniversary Meeting on 5th November 1874, when the following Inaugural Address was delivered by Professor H. Alleyne Nicholson, one of the Vice- Presidents of the Society : INAUGURAL ADDRESS, On the Palceontological Significance of the Migrations of Animals. By H. Alleyne Nicholson, M.D., D.Sc, F.Pt.S.E, F.G.S., Professor of Natural History in the University of St Andrews. The " Introductory Address," which is usually delivered at the commencement of the Annual Session of most learned societies, is very properly intended to be of interest to all the members of the body before which it is given. Hence such addresses usually deal with the internal affairs of the Society itself, or are con- cerned with the current condition of the special science which the Society may happen to cultivate. That the custom here indicated is, in a general way, a good one, I cannot doubt. I am not, however, without the precedent of high authority in departing from this custom to-night ; and I intend, therefore, rather to occupy your attention this evening with a few remarks upon a subject to which, it is true, I have been led by my own special studies, but which, nevertheless, has a general interest for all those who are engaged in the elucidation of geological phenomena. The subject upon which I have chosen to address you to-night concerns the conclusions which may be drawn by the palaeonto- logist from his study of the migrations of animals. This subject has been handled more or less fully by Sir Charles Lyell in his Vol. III. —PART I. A " 2 F.liINliriMJH GEOLOGICAL SOCIETY. great work on the " Principles of Geolop;}'," and has also been ; incidentally treated of by iJarwin in the " Origin of Species whilst Barrande, Edward Forbes, De Yerneuil, and other eminent palaeontologists have drawn attention to it in various portions of their works. In following such distinguished authorities, I do not propose to occupy your attention to any extent with the for the most part well-known facts relating to the migrations of existing species of animals. I may have occasion to summarise some of these facts, but that will be all. On the contrary, I pur- pose to contine my remarks to the bearing of these admitted facts upon various interesting geological and biological questions. I need hardly point out to you the importance of the general subject of the migrations of animals as regards the science of geology. Upon what we believe upon this subject must ultimately depend what we understand by the term " con- temporaneous " as applied to different groups of strata. That the stratified rocks of the earth's crust are, wherever we may examine them, divisible into a succession of definite groups or " formations," is admitted by every geologist. That we cannot compare the successive formations of two different and remote areas except through the organic remains which they may con- tain is also universally conceded. Lastly, it is a matter of general belief, that when we find two formations in widely detached portions of the earth's surface containing the same fossils, or an assemblage of similar and representative forms, then we have to deal with two " contemporaneous " formations. As I have just said, however, all geologists would not attach the same meaning to the term " contemporaneous," and their views upon this fundamental question would depend upon what they believed about the migrations of animals, and of marine animals in particular. The oldest view is one which would attach the natural signification to the term " contemporaneous," and would hold that contemporaneous deposits in different regions were really deposited at precisely the same period. The more modern view, on the other hand, would hold that the word " contem- poraneous," when employed by geologists, is to be construed in a loose sense. Such deposits have not been laid down at the same actual point of time, though, speaking geologically, the interval " which separates them is a small one. They are " homotaxeous deposits and they contain similar fossils, because the animals inhabiting one area migrated extensively into the other. Hence, on this view, two formations containing similar or identical fossils, if placed geographically far apart, would be held in all cases to differ in point of age, the dilference between them being the length of time which would be refpiired for the migration of the aniinals of the odh area to the other, it is obvious, therefore, that the establishment of this exceedingly important view ON THE MIGRATIONS OF ANIMALS. 6 compels us to prove the common, and indeed constant, occur- rence of migrations of animals and plants at all periods of the earth's history, and to this point we shall first turn our attention. We may first take the case, and it is a not uncommon one, in which we find the same species of fossil, or the same group of species, recurring in the uppermost of three related groups of beds, but absent in the middle series ; supposing, of course, that the beds occupy the same area or two areas geographically close together. I may take an example from what we see in the Hudson Kiver group, the Medina sandstone, and the Clinton formation of North America. Here we find the Hudson Eiver deposits, the lowest of the three, to be charged with numerous fossils, amongst which Chcetdes pctropolitanus, Halysitcs catemi- laria, Leptcena sericea, StrojoTioviena alternata, Orthis Mforata, Ortliis testudinaria, and Bellcroplw)i bilobattis, may be mentioned as common forms. All these species reappear in the Clinton formation, the highest of the three groups ; but they have all hitherto proved to be absent from the intermediate formation of the Medina sandstone, though this formation is not absolutely destitute of fossils, and varies in thickness from 100 to over 1000 feet. Precisely similar phenomena, as I have elsewhere shown (" Quart. Journ. Geol. Soc." August, 1872), can be proved to have occurred, if we examine the Graptolites of the iSkiddaw slates, and the Coniston mudstones of the Lake District. Thus, to take two species only, we find Diplograptus pristis and Climaco- grap)tus teretiusculus occurring in the Skiddaw slates, and in the Coniston mudstones, but absent in the intermediate series of the Borrowdale rocks, or Green Slates and Porphyries. Facts of this kind could be readily multiplied, and they do not appear to admit of more than one explanation. When we find the same species present in the same area in two different rock- groups, but absent from the area in sediments intermediate between those groups, we are obliged to suppose that we are deal- ing with a case of migration. At the close of the deposition of the first formation, the species migrated out of the area ; it remained out of it during the whole period occupied in the deposition of the second formation ; and it migrated back again at the commencement of the third formation, when the conditions once more became suitable for its existence. That this is the correct explanation is proved by another con- sideration. We can, namely, often actually find these same species occurring in a different geographical area, in a formation which corresponds in point of age with the inter;nediate and barren formation in the first area. Thus, the zoophytes and mollusca which I have mentioned as occurring in the Hudson Eiver and Clinton formations of the North American continent, 4 EDINBUKGII GEOLOGICAL SOCIKTY.