No. 2.] MATTHEW — POST-PLIOCENE MOLLUSCA. 115 



several small streams come off the hills on the western side of 

 the valley, the whole thickness of the " Leda clay," where these 

 streams cross the railway track, presents a succession of sand 

 beds ; but in tracing these beds in the cuttings along the track 

 of the Railway north or south from the channels of the brooks 

 the sand becomes more and more interlaminated with clayey 

 layer until at length the deposit resumes its normal aspect. It 

 thus appears that when the Leda clay of these valleys was laid 

 down, the tops of the neighboring hills were above water, and 

 as the current from the brooks was sufficient to drive off all the 

 muddy sediment in the waters of the Leda clay sea, at their 

 mouths, the depth of the sea above its present level could not 

 have greatly exceeded 200 feet.* The structure and composition 

 of the beds laid down at this period among the southern hills 

 corroborates the result of an examination of the vertical range in 

 the species of shells which the corresponding deposit at the coast 

 contains. 



Another fact revealed by the examination of these fossils 

 which bears upon the probable depth of the Leda-clay sea is 

 the indication given by the localities of the fossils enumerated 

 in the preceeding list, of a geographical division into two groups, 

 in one of which the species have a more arctic range than the 

 other. Thus on the Bay Chaleur a number of arctic Buccina 

 occur of which only one, B, tejiae, has been recognised in the Bay 

 of Fundy ; and while Nucula tenuis abounds at B.iy Chaleur it 

 has not been found in the clays of the B.iy of Fundy, where its 

 place is supplied by N. expansa. On the other hand several 

 species of the present Acadian marine fauna, such as Lacuna 

 neritoidea, Gardium pinnulatum, and Pecten tenuicostatus occur 

 in the Post-Pliocene of the Bay of Fundy, but have not been 

 found in a fossil state on the Bay Chaleur, though now they are 

 plentiful in its waters. This marked contrast in the grouping 

 of the Post-Pliocene shells of these two bays, cannot be accounted 

 for by differences of latitude alone, but seems rather to have been 

 caused by the existence of a barrier to the free intermingling of 

 the waters of the Bay of Fundy with those of the Gulf of St. 

 Lawrence — a barrier such as would still exist were the interven- 

 ing country depressed to a depth not exceeding one hundred and 

 fifty, or two hundred feet. 



* I have other facts bearing upon this point which will be presen- 

 ted in a future article. 



