:;ns Qoldthwait — Twenty-Foot Terrace and 



Niagara Falls, and seems consistent with commonly accepted 

 estimates. 



The slope of the Micmac terrace, from the foot of the cliffs 

 out to its submerged edge, and its depth there below the Mic- 

 mac water-plane, are significant. Figure 3, plotted from the 

 chart No. 202 (see fig. 2), shows the profile of the Micmac ter- 

 race at Isle Verte and Trois Pistoles. It will be seen that the 

 outer edge of the terrace lies close to the 3-fathom line. Since 

 the tidal range is about 16| feet at Trois Pistoles, the outer 

 edge of the terrace, at present, is covered by about 35 feet of 

 water at high tide. When the Micmac cliffs were being cut 

 back, and the water stood about 20 feet higher than now, the 

 outer edge of the terrace was between 50 and 60 feet under 

 water at high tide. Considering that this was 3 miles off-shore, 

 50 or 60 feet does not seem excessive for the position of the 

 wave base ; in other words, it might be expected that the waves 

 would cut downward 50 or 60 feet on the shelf, while they cut 

 forward 3 miles into the coast. The profile can consistently 

 be regarded as a " profile of equilibrium," developed by erosion 

 on a coast which was neither rising nor sinking. 



There is perhaps some difficulty in explaining why, after this 

 225-mile stretch of coast had risen steadily, though differentially, 

 a few hundred feet, it should remain stationary for a period of, 

 say, 3000 years. One would rather expect to find other cliffed 

 shorelines at higher levels, marking earlier intervals of stability. 

 It is the more puzzling when we seek, further, to explain why, 

 after so long a period of stabilit} 7 , there was a second uplift. 

 Instability seems to have been the condition here during so 

 large a part of post-glacial time, both before and after the Mic- 

 mac stage, that one hesitates to adopt the view that for 3000 

 years or so there was a cessation of coastal movements. 



It might possibly relieve this difficulty to conceive of the 

 earlier, epeirogenic uplifts as having indeed satisfied such deep- 

 seated stresses or temporary isostatic conditions (whatever their 

 origin) as were resident beneath northeastern North America 

 at the close of the glacial period ; and to regard the rest of 

 post-glacial time as a period of approximate stability, compli- 

 cated only by local, seismic movements. There are, indeed, 

 records of several severe earthquake shocks in the Saint Law- 

 rence valley within historic times. In the most severe of these, 

 which occurred Feb. 5, 1663, great rifts were formed in the 

 ground, large landslides took place at the borders of river ter- 

 races, and much damage was done all along the north coast of 

 the Lower Saint Lawrence as far east as Tadoussac. While 

 the record of the shock along the south shore is very meagre, 

 it is known that the quake was felt as far east as Gaspe, and 



