206 THE CANADIAN NATURALIST. [Vol. X. 



Since the deposition of the Leda clays the great change which 

 has taken place in the climate of the district has driven these arctic 

 marine animals northwards into the cold seas above mentioned, 

 and their place has been taken up by a more southern assemblage. 

 The only marine shells of these clay beds living in the Bale de 

 Chaleur now, so far as I have been able to ascertain, are Mya 

 arenaria, L, Mytilus eduUs, L, Macoma fitsea, Gould, vvhich is 

 perhaps identical with M. Groenhindica^ Beck, of Post-Pliocene 

 date, Lunatla heros^ Stimp. and Biiccinum U7idatum, L ; while 

 the following species, the largest proportion of which are of a 

 New England type and do not occur in the Leda clays, so far as 

 known, are now found there: 



Cardium pinmilatuyn, Conrad. 

 Pecten tenuicostatus, Mighels and Adams. 

 JIactra solidisaima, Chemnitz : abundant. 

 Modiola modiolus, Turton ; common. 



M. plieatula. Lam. 



Solen ensis, Lam ; common. 

 Machsera costata, Gould ; rare. 

 Callista convexa, Say ; frequent. 

 Venus mercenaria, Lam ; abundant. 

 Crepidula formicata, Lam : common. 

 Ostrea borealis, Lam ; plentiful. 

 Aporrhais occidentalism Sowerby. 

 Littorinn palliata, Gould. 

 Tectura testudinalis^ Stimp., etc. 



A comparison of this list, meagre as it is, with that of the 

 shells belonging to the Leda clays, given on a previous page, 

 shows at a glance the difference between the faunae of the Post- 

 Pliocene and the Recent periods in the Bale de Chaleur. The 

 amelioration of climate which brought about this change took 

 place along with a rising of the land and a shallowing of the seas 

 around the shores of Acadia. Dr. J. W. Dawson infers, with 

 much probability, that the invasion of Acadian waters by these 

 New England species occurred in the modern epoch. It is a 

 singular fact, ascertained by dredgings made in different parts of 

 the Gulf of St. Lawrence, that that part of it lying to the south 

 of a straight line drawn from Cape Breton to Gaspe, and to which 

 Dr. Dawson has given the name of the Acadian Bay, is inhabited 

 by a colony of marine forms of a southern type (examples of which 

 are found in the Bale de Chaleur) cut off from their relatives on 

 the New England coast by intervening cold waters. To explain 



