No. 2.] MATTHEW — POST-PLIOCENE MOLLUSCA. 117 



the Boulder-clay, and might contain the remains of a few organ- 

 isms capable of withstanding the extreme temperature of an icy 

 sea. The neighboring land would for a time protect this deposit 

 from the action of arctic currents, but as the gradual retrocession 

 of the coastline to the north continued, the polar current would 

 begin to act upon the sea-bottom, and sweep off the finer materials 

 to greater depths in the ocean : deposits formed under these 

 circumstances would resemble the Syrtensian beds. 



From the recession of the glacier zone to the north a further 

 result would follow : the land relieved from the pressure would 

 rise again ; submerged ridges would come near the surface of the 

 ocean and shut off the polar current ; and in the quiet seas and 

 shallow, sheltered sounds and bays thus made, deposition of fine 

 sediment like the Leda clay would proceed. As a final step in 

 the process of re-elevation the sea bottom would reach the tide 

 level, and sand banks and fl its of material like those of the Saxi- 

 <}ava sand would be formed.] 



Following this interpretation of the phenomena of the Post- 

 Pliocene period in Acadia (especially for the Bay of Fundy 

 shores) the history of its marine life would be in brief as 

 follows : 



Original Drift. 



Boulder-clay. — Depression of the present land beneath the ocean 

 about 2000 to 1000 feet — Life meagre and entirly of arctic 

 forms. 



Modified Drift. 



Syrtensian beds. — Depression about 1000 to 500 feet. Present 

 coast line in the Deep-sea-coralline zone. Life probably sparce. 

 Strong ocean currents. 



Lower Leda Clay. — Depression for the tough (lower) clay 

 500 to 200 feet : for the dark (upper) clay 100 to 200 feet. 

 Present coast line in the Coralline zone. Life in the older beds 

 a few deep water species ; in the newer an abundance of marine 

 life. 



Upper Leda Clay. — Depression 100 to 60 feet. Present coast 

 line in the Laminarian zone. Life, fossils less abundant than in 

 the last ; the waters subject to greater disturbance. 



Saxicava Sand. — Depression 40 (or less) to 60 feet. Present 

 coast line in the Littoral zone. Life, molluscs all of shore- 

 loving species. 



