82 THE CANADIAN NATURALIST. [April 



The depressions between these ridges are occupied with Post- 

 pliocene deposits, not so regular and uniform in their arrangement 

 as the corresponding beds in the great plains higher up the St. 

 Lawrence, but still presenting a more or less definite order of suc- 

 cession. The oldest member of the deposit is a tough boulder- 

 clay, its cement formed of gray or reddish mud derived from the 

 waste of the shales of the Quebec group, and the stones and boul- 

 ders with which it is filled partly derived from the harder members 

 of that group, and partly from the Laurentian hills on the opposite 

 or northern side of the river, here more than twenty miles distant. 

 The thickness of this boulder-clay is, no doubt, very variable, and 

 could not be ascertained in the neighborhood of Cacouna ; but at 

 He Verte it forms a terrace fifty feet in height. 



Above the boulder-clay, where it has not been bared by denu- 

 dation, there occurs a dar)s gray, soft, sandy clay, containing 

 numerous boulders, and above this several feet of stratified sandy 

 clay without boulders; while on the sides of the ridges, and at 

 some places near the present shore, there are beds and terraces of 

 sand and gravel, constituting old shingle beaches apparently much 

 more recent than the other deposits. 



All these deposits are more or less fossiliferous. The lower boul~ 

 der-clay contains large and fine specimens of Leda truncata and 

 other deep-water and mud-dwelling shells, with the valves attached. 

 The upper boulder-clay is remarkably rich in shells of numerous 

 species; and its stones are covered with Polyzoa and great Acorn- 

 shells (B -di mus Humeri), sometimes two inches in diameter and 

 three inches high. The stratified gravel holds a few littoral and 

 sub-littoral shells, which also occur in some places in the more 

 recent gravel. On the surface of some of the terraces are con- 

 siderable deposits of large shells of Mi/a truncata; but these are 

 modern, and are the ' kitchen-middens ' of the Indians, who in 

 former times encamped here. 



Numbers of Post-pliocene shells may be picked up along the 

 shores of the two little bays between dcouna and Riviere-du- 

 Loup ; but I found the most prolific locality to be on the banks of 

 a little stream called the Petite Riviere-du-Loup, which runs 

 between the ridge behind Cacouna and that of Mount Pilote, and 

 empties into the bay between Riviere-du-Loup and the pier. In 

 these localities I collected eighty-four species, about thirty-six of 

 them not previously published as occurring in the Post-pliocene 

 of Canada. A list of these fossils is appended to this paper ; and 



