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 Cbaleur 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. 



