246 THE CANADIAN NATURALIST. [Vol. vi. 



more or less by the ice every winter, so that the tracks cleared 

 by the people for launching their boats and building their fishing- 

 wears, are in a few years filled up. Wherever such boulders are 

 dropped on banks of clay in process of accumulation, a species of 

 Boulder-clay, similar to that now seen on the land, must result. 

 At present such materials are deposited under the influence of 

 tidal currents, running alternately in opposite directions; but in 

 the older Boulder-clay period, the current was probably a steady 

 one from the north-east, and comparatively little affected by the 

 tides. 



The Boulder-clay of Cacouna and Biviere-du-Loup, being at a 

 lower level and nearer the coast than that found higher up the 

 St. Lawrence valley, is probably newer. It may have been de- 

 posited after the beds of Boulder-clay at Montreal had emerged. 

 That it is thus more recent, is farther shown by its shells, which 

 are, on the whole, a more modern assemblage than those of the 

 Leda clay of jMontreal. In fossils, as well as in elevation, these 

 beds mare nearly resemble those on the coast of Maine. It would 

 thus appear that the Boulder-clay is not a continuous sheet or 

 stratum, but that its different portions were formed at different 

 times, during the submergence and elevation of the country ; and 

 it must have been during the latter process that the greater part 

 of the deposits now under consideration were formed. 



The assemblage of shells at Biviere-du-Loup, is, in almost 

 every particular, that of the modern Gulf of St. Lawrence, more 

 especially on its northern coast. The principal difference is the 

 prevalence of Leda truncata in the lower part of the deposit. 

 This shell, still living in Arctic America, has not yet occurred 

 in the Gulf of St. Lawrence, but is distributed throughout the 

 lower part of the Post-pliocene deposits in the whole of Lower 

 Canada and New England, and appears in great numbers at 

 Biviere-du-Loup, not only in the ordinary form, but in the 

 shortened and depauperated varieties which have been named by 

 Beeve L. sillqua and L. sulcifera. 



0^ Astarte Laurentlana, supposed to be extinct, and which 

 occurs so abundantly in the Post-pliocene at Montreal, few speci- 

 mens were found, and its place is supplied by an allied but appa- 

 rently distinct species, to be noticed in the sequel, which is still 

 abundant at Gaspe and Labrador, and on the coast of Nova 

 Scotia. 



It must be observed that though the clays at Biviere-du-Loup 



