﻿THE CURRENTS OF THE OCEAN. 141 



in outline and composition. In these respects there is a striking uniformity in the coast, 

 while in the interior the geological diversities allow a wide range of dissimilarity. The 

 keys and banks of the Florida coast, in which the deposit of sand is mixed with that of 

 the coralline detritus, are to be considered on another occasion. Beginning, then, from 

 the southern extremity of Georgia, and proceeding northward, there is a belt, of variable 

 breadth and of loose material, the leading distinction of which is that it has been for a 

 long time subjected to the action of water. This quality is so prominent as to create a 

 uniformity of appearance independent of mineralogical composition, showing that it is 

 the mechanical, rather than the chemical, properties which give the predominant character 

 to these formations. A part of these alluvial deposits is formed and remains under water, 

 as, for example, the Nantucket Shoals. But there are also, at a distance from the Ameri- 

 can continent, towards the northeast, very large subaqueous deposits, as George's, New- 

 foundland, and other banks, resembling the banks and shoals near the coast in structure 

 and material, to which we are naturally led to apply the same laws of origin and formation. 

 The idea of such a connection is not controverted by the distance apart, and apparently 

 distinct separation, of the great banks; for the smaller banks and shoals near the land are 

 divided by valleys of proportionate depth, having for their bottom mud, gravel, and large 

 drift, teeming with animal life, in which the shoals themselves are wholly deficient. 



Taking the whole of these sandy formations in one view, and considering them 

 in relation to the continent, it will be remarked that a comparatively narrow and compact 

 apex at the south spreads towards the north and east into a broadly diffused and uncon- 

 nected series of deposits, and that throughout this extent all the minor varieties of geo- 

 graphical division are met with. But the greatest amount of the material is collected at 

 the north and east, in which direction it seems to have been carried as to a place of 

 final rest. A line traced with a free hand through this space will be the arc of a 

 quadrant nearly, the abscissa being somewhat longer than the ordinate, and this upon 

 examination proves to be the general course of the tide-wave on this continent. The 

 effect of that undulation which rises in the Bay of Fundy will be noticed subse- 

 quently. 



The progress of the great tidal wave of the Atlantic is from south to north ; the 

 cotidal lines, or lines representing the summit or ridge of the tide-wave, drawn between 

 places on both sides of the ocean that have high water at the same time, being (speak- 

 ing in general) at right angles to the meridians. These lines are curves, convex in the 

 direction of their motion, in consequence of the retardation of their extremities by the 

 shores of the continents. The effect of this retardation is to create those numerous 

 tidal currents, and various conditions of rise and fall, of conflict and interference, which 



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