. La Canadian field-naturaliste. 212 Le Canadian Field-Naturalist [Vol. XLII. Figure : Mesidotea sabinei. La taille naturelle. La figure montre le outHne de la concrétion dans le centre de ce crustacé qui a été trouvé. large gamme de salinité. Macoma balthica qui est probablement le plus commun des combustibles dans la vallée d'Ottawa conclut-il normal habitatin les eaux saumâtres de la mer Baltique. Ce shell et ses associés indiquent pour le bras de la vallée d'Ottawa Le SPEIJ- tocene dans la mer où ils vivaient un degré modéré de la salinité, comparable à celle de la partie supérieure de la Baltique. Les gastropodes sont rares

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. The Canadian field-naturalist. 212 The Canadian Field-Naturalist [Vol. XLII. Figure: Mesidotea sabinei. Natural size. The figure shows the outHne of the concretion in the centre of which this crustacean was found. wide range of salinity. Macoma balthica which is probably the most common fossil in the Ottawa valley finds it normal habitatin the brackish waters of the Baltic Sea. This shell and its associates indicate for the Ottawa valley arm of the Pleis- tocene sea in which they lived a moderate degree of salinity, comparable with that of the upper Baltic of the present. Gastropods are rare in this fauna. Such typical marine creatures as sea urchins are wanting also. Brachiopods which require water of ordinary marine salinity are unknown in the Pleistocene deposits of the Ottawa valley. The relatively small number of species known from the Ottawa valley fades as compared with the considerable number known in the lower St. Lawrence basin clearly points toward the unfavourable low salinity conditions of the former for typical marine creatures. In Ami's lists of the Ottawa Pleistocene the mol- lusca are represented by only 40 species while in the lower St. Lawrence region Dawson found 340 species in this fauna. In its arctic and sub- arctic range M. entomon affords evidence supple- menting that of Saxicava arctica, Porilandia gla- cialis (Wood) (P. arctica) and others of the molluscan fauna with which it is associated in suggesting climatic conditions approximating those of the Ottawa valley marine clays. Port- lavdia glacialis which is such a characteristic fossil in the Pleistocene clays of Eastern Canada has not been found south of the Strait of Belle Isle according to Whiteaves. Saxicava rugosa is a characteristic Arctic shell, though having a considerable southern range. The writer found it in such abundance as to nearly exclude other species in lat. 74.15 West Greenland on a mud bottom in front of Cornell glacier. LANDSLIDES IN CANADA^ By D. A. NICHOLS THIS PA

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