No. 6.] MATTHEW — TIDAL EROSION. 369 



and boulders swept from the land. But though the Bay of 

 Fundy is deep and is sheltered from the great ocean currents, 

 the bottom in its deeper parts does not usually consist of mud, 

 but of sand and coarser materials. The cause of this anomaly 

 is apparent when we examine the action of the tidal currents 

 upon the bottom of the Bay. 



The sections of the North Atlantic between New York and 

 Bermuda, and Halifax and Bermuda respectively, projected from 

 the soundings of the Challenger, shew where the tidal impulse 

 passing through the ocean is converted into a wave pressing up 

 along the submerged border of the continent ; and the form of 

 the bight or indentation of the coast between Cape Cod and 

 Cape Sable, called the Gulf of Maine, has the effect of com- 

 pressiog this wave laterally and driving it onward toward the 

 entrance to the Bay of Fundy. From the shallowness of the 

 sea from George's Banks westward toward Cape Cod, it is evident 

 that the power of the rising tide is greatly broken in the western 

 part of the Gulf of Maine ; and that the tidal impulse which 

 gives rise to the Bay of Fundy tides is propagated chiefly 

 through the deep channel between George's and La Have banks. 

 Off Cape Sable the tide attains a speed of IJ- knots (which 

 in tides is a wearing pace), and thence sweeps around into the 

 Bay of Fundy,-'' 



The apparent width of the Bay at its mouth is considerable, 

 but the actual width of the deep-water passage is not great, as 

 the shoals and reefs connected with the island of Grand Manan, 

 block a large part of the opening. Owing to this the great tidal 

 wave which enters the Bay twice a-day, is compressed between 

 the Old Proprietor Ledge off Grand Manan and the North-west 

 Ledge off Bryer Island into a space of 24 geographical miles, of 

 which ^0 miles has an average depth of 100 fathoms, with a 

 bottom of rock, sand and gravel. Here the tide runs at the rate 

 of three miles an hour, but immediately the strait is passed mode- 

 rates its pace, the rocks and gravel disappear and the bottom 

 becomes more sandy. On the north side of the Bay, this sandy 

 condition of the bottom is found only in the deeper parts, and 



* The influence of the G-ulf of Maine on the tides of the Bay of 

 Fundy may be inferred from the fact that unusually high tides in 

 the Bay are generally accompanied by S.E. winds, not by S.W. winds 

 as might be supposed likely from the direction towards which the 

 Bay of Fundy opens. 

 Vol. IX. X No. 6. 



