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BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA VOL. 60, PP. 363-380. 4 PLS. FEBRUARY 1949 POST-PLEISTOCENE CONNECTION BETWEEN JAMES BAY AND THE GULF OF SAINT LAWRENCE BY'A. LA ROCQUE CONTENTS Page Abstract 363 Introduction 364 Acknowledgments 364 Potter's argument 365 Critique of Potter's argument 366 Geologic objections to the western routes 368 Path of recession of the Wisconsin ice sheet 368 Lake Barlow-Ojibway 368 Chronology of uplift 369 Consequences of the assumed connection 369 Boundaries of the Champlain Sea 370 Paleontological objections to the western routes 371 Character of the Pleistocene fauna 371 Invasion of new marine areas 371 Lake Saint John route 373 General discussion 373 Path of recession of the Wisconsin ice sheet 374 Lake Barlow-Ojibway 375 Chronology of uplift 376 Consequences of the assumed connection 376 Boundaries of the Champlain Sea 377 Paleontological objections 377 Invasion of new marine areas 378 Conclusions 378 References cited 378 ILLUSTRATIONS Figure Page 1.—Early (Low) marine stage in eastern Ontario 374 2.—Maximum marine stage in eastern Ontario 375 3.—Conditions shortly after the draining of Lake Ojibway 376 4.—Possible marine connection between Lake Saint John and James Bay when the ice front had retreated from part of James Bay 377 ABSTRACT To explain the distribution of certain modern halophytic plants on the shores of James Bay, Potter advanced the idea of a post-Pleistocene marine connection between James Bay and the St. Lawrence drainage; he placed his seaway between Lake Timiskaming and James Bay. Potter's route is considered improbable because of 363 Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/60/2/363/3426328/i0016-7606-60-2-363.pdf by guest on 30 September 2021 364 A. LA ROCQUE—POST-PLEISTOCENE CONNECTION geological and paleontological objections, which are discussed in detail. Another route, between Lake St. John and James Bay, is advocated and arguments advanced to show that it is not open to the objections against the route chosen by Potter. INTRODUCTION Geologic evidence is not confined to facts derived from a study of the rocks, their attitude, their lithologic composition, or the fossils which they may contain. This is especially true of the evidence for the history of the Pleistocene and post-Pleistocene. An interesting example of the unexpected quarters from which geologic evidence may be obtained is a paper by Potter (1932) which seeks to explain the unusual distribution of certain plants by means of a post-Pleistocene connection between James Bay and the St. Lawrence drainage. Potter's approach to the problem was botanical or more exactly phytogeographic but his conclusions are important to the geologist. His incidental use of evidence drawn from the distribution of the mollusca is of interest; consideration of this aspect of the subject attracted the writer to the problem. The idea of a connection between James Bay and the St. Lawrence drainage was not new, although Potter seems to have been unaware of the fact. According to Coleman (1922, p. 57), Sir J. William Dawson assumed such a connection to explain most of the glacial phenomena of Ontario and Quebec. Dawson's theory has never found much favor with glacial geologists and had been forgotten long before Potter sought to explain the unusual distribution of his plants. The following paragraph (Coleman, 1922, p. 57) summarizes Dawson's theory and the prevalent opinion of glacial geologists concerning it a few years before Potter attacked the problem from a new approach: "Dawson explained most of the glacial phenomena of Ontario and Quebec by assuming that the watershed between the St. Lawrence system and Hudson bay was lowered sufficiently to open a broad strait between the Champlain sea and an enlarged Hudson bay or sea. Through this channel he supposed that a powerful current like that off the coast of Labrador swept icebergs and floe ice from the Arctic regions, lowering the temperatures of all eastern Canada. He believed that the boulder clay of the Pleistocene was formed by floating ice and not by a Labrador ice sheet moving toward the south. This view is no longer held by any glacial geologist...." Dawson's seaway might have remained in the limbo of discarded theories had not Potter sought to explain the distribution of his plants, but the objections which led glacial geologists to discard Dawson's theory are equally valid in disproving Potter's assumed route for a marine connection between James Bay and the Champlain Sea. If Potter's statement on the distribution of his plants is correct, his reasoning justifies a re-examination of the whole question and a careful investigation of the possibility of interpreting the geologic facts to harmonize with the botanical evidence presented by Potter. ACKNOWLEDGMENTS The writer is indebted to Professor George M. Stanley of the University of Michi- gan who suggested the problem to him, to Dr. Henry van der Schalie of the Museum Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/60/2/363/3426328/i0016-7606-60-2-363.pdf by guest on 30 September 2021 ACKNOWLEDGMENTS 365 of Zoology, University of Michigan, for information concerning the significance of molluscan assemblages, to Dr. Richard F. Flint for valuable suggestions for the im- provement of the manuscript, and to Dr. Nicholas Polunin, Macdonald Professor of Botany, McGill University, Montreal, Canada, for valuable information concerning the plants involved. The maps have been prepared'by Mr. Norman J. Willimovsky of the Museum of Zoology, University of Michigan. POTTER'S ARGUMENT During the summer of 1929, Potter (1932, p. 70) collected the following species along the shores of Hudson Bay and James Bay: Zannichellia palustris L. var. major (Boenn.) Koch, Glaux maritima L. var. obtusifolia Fernald, Juncus Gerardi Loisel., Carex maritima O. F. Mueller, Carex norvegica Willd., Carex glareosa var. amphigena Fernald, Plantago juncoides Lam. var. decipiens (Barneoud) Fernald, Poa eminens J. S. Presl, Scirpus rufus (Hudson) Schrad. These are strict halophytes, that is, plants which will live only near salt water. Potter has given maps showing the distribution of each of these plants in North America. The most important facts about their distribution are: (1) "In no case have these plants been reported as growing along the shores of Hudson Straits or along the northernmost Labrador coast. Four of them have been rarely found north of Hamilton Inlet; two reach their northern limits hi Hamilton Inlet; and five are not known north of the Straits of Belle Isle." (Potter, 1932, p. 71). (2) The absence of records of these species cannot be explained by the lack of collecting according to Potter, but see my Critique of Potter's argument. (3) The plants in question are not found inland between James Bay and the Saint Lawrence River. The latter was to be expected, since they are strictly or primarily maritime. In addition to the strict halophytes enumerated above, Potter also lists the follow- ing indifferent halophytes which live in association with the former, but whose dis- tribution can be explained without bringing extraordinary agencies into play: Potamogeton filiformis Pers., Triglochin maritima L., T. palustris L., Scirpus ameri- canus Pers., Juncus balticus Willd., var. littoralis Engelm., Potentitta Anserina L., Myriophyllum exalbescens Fernald, Lathyrus maritimus (L.) Bigel., Arenaria pep- loides L., Mertensia maritima (L.) S. F. Gray, Bidens hyperborea Greene, an estuarian species, and Zostera marina L., a plant confined strictly to salt water. Potter considers three main explanations of the dispersion of these plants: (1) Driftless areas may have harbored them during the Wisconsin glaciation; (2) dis- persal by wind, animals, birds, or water since the recession of the last ice sheet; (3) migration along the shores of a marine connection between the St. Lawrence Basin and James Bay. He discards the first two possibilities for the following reasons: 1. Driftless areas: "Nowhere along the coasts or on the islands of either James Bay or southern Hudson Bay have areas been discovered which escaped the ruthless work of the Wisconsin ice sheet." 2. (a) Wind: "In the case of plants establishing intermediate stations between Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/60/2/363/3426328/i0016-7606-60-2-363.pdf by guest on 30 September 2021 366 A. LA ROCQUE—POST-PLEISTOCENE CONNECTION two points it is difficult to apply this method of migration to halophytes over areas not favorable to salt-loving plants." (b) Animals other than birds: Fish, amphibia, and reptiles play a very small part in the dissemination of plants. The species in question do not possess seeds so modified as to attach to fur of mammals. "Human travel has not been very great between these two regions and we can scarcely look to this source as the means of introduction. Had these plants any food value or other economic significance, human migrations would of necessity have to be investigated." (c) Birds: Bird authorities agree that birds seldom carry seeds of plants, ". and the indisputable evidences of birds carrying seeds either in them or adhering to them mentioned in books evidently apply to birds shot at or not far from, their daily haunts, and not to such as have just made a long journey." (d) Water: The marine waters along the coast of Labrador and Hudson Straits into Hudson Bay were not the route of migration, for, if they had been, the plants should be found in at least a few places along the coast; they are not. Migration via. fresh water up the streams of the St. Lawrence drainage, over the height of land into the Hudson Bay drainage, is improbable for halophytes. His only remaining alternative, Potter believes, is migration along the shores of a marine connection between the two bodies of water.