84 THE CANADIAN NATURALIST. [April 



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 Riviere-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 

 deposited 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 Montreal. In fossils, as well as in elevation, these 

 beds more 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 Riviere-du-Loup is, in almost every 

 particular, that of the modern Gulf of St. Lawrence, more espe- 

 cially on its northern coast. The principal difference is the pre- 

 valence 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 Riviere-du- 

 Loup, not only in the ordinary form, but in the shortened and 

 depauperated varieties which have been named by Reeve L. siltqua 

 and L. sulci f era. 



Of Astarte Laurentiana, supposed to be extinct, and which 

 occurs so abundantly in the Post-pliocene at Montreal, only one 

 valve was found, and its place is supplied by the allied but appa- 

 rently distinct species, A. comjyressa, which is still abundant at 

 Gaspe and Labrador, and on the coast of in ova Scotia. This 

 exchange of A. Laurentiana for A. compressa is on these coasts 

 an unfailing evidence of less antiquity. 



A study of the varietal forms under which common species 

 occur, also leads to the same conclusion as to the less comparative 

 antiquity of these beds ; but this is a very curious and intricate 

 question, on which I have accumulated a great number of facts 

 which I propose to publish at a future time. 



