96 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
antecedent origin for the Halfway River Pass, but he has not brought 
that hypothesis into relation with a coherent scheme of physiographic 
development for the whole region. 
Dissection of the Tertiary Peneplain; Drowning and More 
Recent History of Acadia. 
This peneplain of the second cycle was uplifted probably with differen- 
tial movement during the later Tertiary. A new, third cycle was thus 
introduced, and numerous valleys were sunk to considerable depths 
beneath its surface. This cycle has been interrupted several times by 
changes of level, the most significant of which was the positive movement 
of sea-level whereby the lower courses of many of the rivers have been 
drowned. In this way, the valleys of the Miramichi, Richibucto, Buc- 
touche, Shubenacadie, Avon, and other rivers have been turned into 
tidal estuaries. The trends of the valleys opening into the eastern end 
of the Bay of Fundy seem to show that these valleys belong to one 
great river-system. This has since been drowned probably by the same 
wholesale down-sinking that explains the estuaries of eastern New 
Brunswick, and of the Nova Scotian seaboard. In the light of present 
knowledge, it cannot be definitely stated whether Northumberland Strait 
represents part of a drowned river-valley or the locus of a northwest- 
southeast trough due to crustal warping. Just how far such warping 
has affected the Tertiary peneplain cannot be made out without better 
topographic data, better maps, than we now have at command. 
The general depression of Acadia developing the estuaries was followed 
by an elevation of varying amount in different areas. The post-glacial 
marine plain of Middleton dates from this last uplift. Much more 
extended coastal plains of the same age fringe Chaleur Bay, the whole 
eastern coast of New Brunswick, and the coast of Maine. 
Still more modern are the famous tidal flats of the Fundy trough, the 
sand-beaches and bars and the dune-belts of the coast, the fine palisade- 
like cliffs which the waves, aided powerfully by tidal scour, are driving 
inland, and the resulting marine benches of. Minas Basin, Chignecto 
Channel (Plate 8), and of the Bay of Fundy proper. Excavation by 
tidal scour is now going on apace at Minas Channel, at Digby Gut, 
and at the passes on the southwest, where all these gates are every day 
opening wider. 
