﻿146 GEOLOGICAL ACTION OF 



coast of Norfolk and Suffolk ; the other, on the southern shores of Norway. The first of 

 these instances occurs at the meeting of tides arriving in opposite directions along two 

 different channels, and this meeting is pointed out by the crowding together of the co- 

 tidal lines, or, in other words, by the rapid change in the tide-hours due to the impeded 

 progress of the tide-wave. Between Yarmouth and Southwold, the least range of the 

 tide is two or three feet, while the greatest range is only seven or eight feet. But at 

 points on each side of these stations, and not far distant from them, the greatest range 

 of the tide rises to twenty feet. (See Whewell's Researclies on the Tides, Sixth Series.) 

 The changes that have taken place on this part of the English coast have been described 

 in detail by Sir Charles Lyell, and M. Beaumont. It is not necessary to repeat here 

 what has been said concerning them, but it must be admitted that they support in a 

 satisfactory manner the view that the amount and locality of alluvial deposits are in certain 

 cases determined by the interference or convergence of opposing tide-waves, and de- 

 pendent in a measure also upon the motion of the tidal currents, of which the average 

 rise and fall of the tides may be taken as an exponent. 



The subaqueous deposits, or banks, off Yarmouth result from the same causes. The 

 alluvial formation in the Wash is an instance of bay deposit. 



With regard to the sandy region on the southern coast of Norway, of which Chris- 

 tiansand is the principal depot, it is to be observed that Stavanger is a point of diver- 

 gence, from which one portion of the divided tide-wave travels sluggishly along the south 

 shore, until, at Christiansand, the greatest range of the tide is only one foot. It is a 

 probable inference from the principles laid down, that the deposit in this region is owing 

 to the conflict of the feeble tidal current corresponding to this tide-wave with the con- 

 stant current that flows out of the Baltic. 



This current always sets to the westward along the shore, but its force must be 

 gradually overcome by the pressure of the tidal current, which becomes more sensible 

 as it proceeds to the westward. It is further to be remarked, that the currents created 

 by the winds on the southwest coast of Norway run much stronger to the south than 

 they ever do to the north. 



The Landes of France, at the bottom of the Bay of Biscay, is another region of 

 sand too well known to geologists to need description. It is an instance of the bay 

 deposit on a large scale, as Holland is of the sound deposit. It lies in the place to 

 which the material should be carried by the tide, which, turning round Cape Ortegal, 

 makes the circuit of a great bay. The original form of the bay, at the beginning of 

 the present era, was deep and pointed towards the bottom, and thus particularly suited 

 to create numerous interferences resulting in eddies, and in that state of rest in which 

 the water readily drops its freight. 



