266 THE QUESTION OF SUBSIDENCE 



position is such that the beach to the north of the pond might 

 well serve it as a glacis. 



From the Maurepas Bastion towards the south, a wall, a 

 moat, and another bastion — the Bourillon — completely covered 

 the neck of the isthmus at this point. 



Although any argument based on a comparison of the 

 heights of the pond and of ordinary high tide, must necessarily 

 be inconclusive as to the question of subsidence, still the 

 hypothesis does not derive support from the fact that the bot- 

 tom of the sluiceway, at the western extremity of the pond, is 

 now sufficiently high to carry away the waters of the pond at 

 all but abnormally high tides. 



At present, however, a barrier of sand and stones lies across 

 the point of exit, and the drainage of the pond is by liltration 

 through the gravel of the beach, and this latter fact gives rise 

 to some reflections of a general character. 



In the case of ponds along the ocean shore, separated from 

 the ocean by a beach, and into which no brook of any consider- 

 able volume empties itself, this percolation through the sand is 

 sufficient in the ordinary case to prevent the waters of the 

 pond from overflowing the beach. We have frequently observed 

 cases of this kind. And it may, too, be observed, that in the 

 case of any particular pond of this class, a certain fixed relation 

 exists, under normal conditions, between the height of the 

 water in the pond and the mean level of the ocean water outside. 



The waters of the Bras d'Or Lake as compared with the 

 Atlantic Ocean, although a regular channel connects them, are 

 subject to this very law, and the stone structure at the St. 

 Peter's canal locks is arranged with regard to this condition. 



The reasons for this state of things are to my mind so plain 

 that I do not consider it necessary to explain them. 



I trust I am not making too long a step in the reasoning 

 Process here introduced if I state that any elevation of the 

 Atlantic Ocean with reference to the Island of Cape Breton, or 



