﻿THE CURRENTS OF THE OCEAN. 125 



There is another mode of constructive action, which, being finally exhibited partly 

 above water, can be more easily traced in its progress, and which at the same time ena- 

 bles us to form an approximate idea of the rate of increase of the shoals. This mode 

 is founded upon an action of the tidal currents which may be thus explained. A tidal 

 current freighted with suspended matter, and eddying round a bold point, is interrupted 

 and changed in its course by the projecting tongue or prominence at which it turns, and 

 will leave there constantly a part of its burden, this prominence serving as a nucleus to a 

 shoal or bar joined to the land, in the same manner as the inequalities of the bottom to 

 the insulated shoal at sea. The subsequent gradual elevation of the shoal above the 

 water is due to the influence of the winds. 



It will be seen by looking at a map of the coast of the United States from the high- 

 lands of Navesink to the extremity of Cape Cod, that one normal form is constantly 

 repeated. It is that of a projecting point lying in a generally north and south direction, 

 and inclosing a bay of greater or less extent. That point on the New England coast 

 called Cape Cod being the best known, I will refer to it as the type of this formation, 

 which is repeated in the Great Point of Nantucket, in Cape Poge (Martha's Vineyard), 

 and in Sandy Hook (New York harbour). There are also numerous small points, pre- 

 cisely similar in outline and relation to the local current, to be found in the harbours of 

 this part of the coast. The tide passing along the outer shores, against which it presses 

 with accumulated force, eddies around the extremity of the point, and expands in the 

 inclosed space, where its velocity is lessened by diffusion. 



Cape Cod is so large that it can only be examined as a whole on the map ; but the 

 small points, in the formation of which the principle is equally illustrated, are easily com- 

 prehended in a single view, while something can generally be learned of the rate of 

 their formation from the residents in their neighbourhood. 



As the original settlers of New York brought with them from their native alluvial 

 shores the name which they transferred from the Hoek von Holland to the sea boundary 

 of New York Bay, and as this name is literally significant of this very common form of 

 alluvial deposit, I adopt the title as a generic term. 



The tidal current, as has been said, after passing one of these points, falls into eddies 

 on the inside. These eddies are favorable to an accumulation of the suspended matter, 

 and may also be supposed to control its form. This mode of accumulation is a familiar 

 one to engineers. In the rivers Aar and Rhone, walls projecting into the current are 

 built expressly to obtain a new soil by creating eddies, the sedimentary matter being 

 collected in large quantities by these eddies in one place. It is also understood and prac- 

 tised by our own engineers. At sea-walls and breakwaters the same effect is observed ; 



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