RIPPLE MARKS EPRY. 313 



accompanying instantaneous photograph (fig. 11). A wave has 

 broken under precisely these conditions. One can discern still the 

 contour of the fringe of foam that it spreads out on the beach. 

 Being violently thrown from left to right, it has already abandoned 

 the left portion. The obliquity of its course is revealed, in part, 

 at least, by the direction of the line of shadow, which, at the right, 

 marks the elevation which it forms on mingling with the succeeding 

 wave, which latter at this point has not itself undergone any devia- 

 tion. Wliere the receding wave has passed are displayed the fea- 

 tures of ripple marks. 



In general, as we have established in the bottom of our little 

 pool at Pouldu, ripple marks arrange themselves parallel with the 

 line of the shore, under the predominating influence of the trans- 

 verse current, which draws the sands toward the outlet. On the 

 contrary, the direction of the ephemeral marks outlined here (fig. 11) 

 approach much more closely to a perpendicular than to a parallel 

 with this line. The reason of this difference is very simple. It 

 lies in the fact that this instantaneous photograph was taken on 

 the upper beach. There only the action of the normal reflex cur- 

 rent which levels the sand ordinarily exerts itself. It is owing to 

 a quite special circumstance that accidentally the effects of the de- 

 scending current were altered for a few seconds to a slight degree. 

 The direction of the ridges formed express the relation between the 

 two forces which acted together at this place. 



But let us not make a point of this photographic document which 

 was obtained with difficulty, and may doubtless appear insufficiently 

 clear and convincing, moreover, as the jurists say, " Testis itnus testis 

 nulhcs,^'' and as we have not been able to obtain any other evidence of 

 this kind, we shall content ourselves with arguments derived from 

 ripple marks which, like those of Pouldu, have acquired their definite 

 form. In whatever place one observes them there are such numerous 

 and harmonious evidences in favor of our theory that they appear to 

 us irrefutable. 



We now present an illustration of three conditions of the sand in 

 the Bay of Somme (fig. 12). The waters first descended vertically 

 down the slope of the upper beach directly toward the spectator, then 

 at a certain moment they ran obliquely to reach the rivulet at the 

 right, between the piles of the wharf, that should direct them toward 

 the sea. The first slope, where ordinarily the action of the receding 

 water alone exerts itself, is leveled. The less-inclined slope of the 

 intermediate area, on the contrary, is covered with ridges due to a 

 double action, the preponderating one of the transverse current and 

 the diminished action of the normal current. 



Again, in figure 13, we have, seen from above, that marvelous whirl- 

 pool of Trieux, dominated by the chateau of Roche-Jagu and its 



