﻿|;; ( ; GEOLOGICAL ACTION OF 



by the waves beyond the reach of common tides, and, there heaped up, they form a natu- 

 ral sea-wall defending a trad of meadow land from the encroachments of the water. 

 The structure of the wall <>n the land side affords a striking evidence of the pro- 

 jectile force of the waves. Owing t<> s • causes thai give them a greater violence 



in certain directions, thej have bo crowded up the stones that in some places they stand 

 like abutments to the inside wall. Bui the part performed by the waves is merely to 



acc |,|,. ||| ( . materials in masses. It is the currents that transport the materials in 



(heir course, and decide their position; the be Si proof of this is the fact, that on 

 the opposite side of tin: cliff there is no sea-wall, although there the action of the storm 



is equally felt. It mighl he objected, that the tidal currents are incapable of moving such 

 heavy weights; but, besides the proofs afforded by the relative positions of the wall and 

 cliffs, some facts will be brought forward hereafter which will remove this objection. 



It. has been suggested, and I have loubt correctly, thai the kelp on the rocks assists 



the action of the currents by the large and buoyant surface it presents to their force. 

 IY1. Elie de Beaumonl has described the appearance of several similar formations; one, 



particularly, at Dieppe. In thai instance, also, the source of the materials. which form 

 the seawall (levie de gakts) is situated on thai side from which the flood tide ap- 

 proaches. The tide rises to a greater heighl here than in Boston harbour, and the stones 

 are transported by the current with such facility and in such abundance, that it has been 



found requisite tO construct artificial walls, and contrive a plan for washing the channel 

 by the river, in order In keep open the port. 



1 1 follows, therefore, thai these sea-walls, though owing their actual form to the. waves 



that keep the materials on the shore, o\\ e equallj their position to the currents, which, 



transporting the materials from the place where they have fallen into the sea, bring them 



where they will be subject to the action of the waves in storms. 



When the beach is composed of light, silicious sand, easily transported by the wind, 

 the phenomenon of dunes or downs appears. They are hills consisting altogether of 

 light particles of sand, deposited by the tide, which, being exposed at low water, dries, 

 and is blown Up above the reach of the sea. The dune formations are immediately 

 known by their peculiar figure. The top is smooth and rounded, sloping gently towards 

 the quarter from which the sand comes, and steep and irregular on the opposite side. 

 They are, however, too will known to require a particular description here, though they 

 are SO prominenl a feature of a sandy region, that it would not be proper to pass them 

 over entirely. M. de Beaumont has given the fullest details concerning their rise and 

 progress, showing how the) advance by successive steps into the interior, render sterile 

 the soil which they invade, and overwhelm villages in their path. Sometimes, indeed, 



