316 ANNUAL BEPORT SMITHSONIAN INSTITUTION, 1913. 



that they never form in the angle? Not at all. I have seen them 

 sometimes, but when a strong wind from the west forces the water to 

 the right, parallel with the shore into the depressions of the embank- 

 ment. 



I could multiply the examples indefinitely, accumulating the evi- 

 dences, but this article would then be nothing more than an album of 

 photographs. I shall not dwell on the evidence further, considering 

 sufficiently demonstrated a fact that anyone, if I have failed to 

 remove his doubt, can easily confirm on any beach. In concluding, 

 I desire to return to two secondary points, but not unimportant ones, 

 which, after mentioning incidentally, I put aside temporarily in order 

 to first settle the principal questions. The secondary questions relate 

 not to the mode of formation of ripple marks but to their location 

 and the differences that are observed in their dimensions in the vari- 

 ous places in which they appear. 



Eipple marks, as I have observed, form only on the lower beach, 

 and there again not in all places nor at all times. I will explain 

 why none are seen in the photograph taken on the beach at Fort 

 Bloque. To account for their absence in this part of the bay of 

 Goulven, shown in figure 5, which includes all portions of the ripple- 

 mark field, it is necessary to take notice of a factor that has not as 

 yet been mentioned. This is the nature of the bottom. Here we 

 encounter a layer of mud and not of sand. It is not necessary to 

 seek for any other reason why the ripple marks are absent. They 

 do not form on muddy bottoms. Such bottoms, which are very 

 compact because composed of very fine particles, oppose to the attack 

 of the tide a resistance all the more effective as their surface is 

 viscous and gummy. The sea strikes them without finding more to 

 take hold upon than the wind finds on a surface of water protected 

 by a film of oil. A current may, however, if it be very violent, 

 leave some trace of its passage, but indistinct and of little im- 

 portance. In place of ripple marks one observes that kind of choppy 

 appearance, like the coagulations in a semiclear soup, which one sees 

 in figure 5. It is of interest to compare the effects produced by the 

 same current under exactly the same conditions in two places near 

 Lesconil, distant scarcely 100 meters from one another, in the one 

 case on mud (fig. 18) and in the second on sand (fig. 7). 



Between the mainland and the island of Oleron the rapid cur- 

 rent of Maumusson produces on the coarse sands from the point of 

 Menson to the St. Trojan landing, ripple marks of enormous size 

 in the furrows of which on the days of the spring tide one spears 

 sole, turbot, plaice, torpedoes, and gurnards. But beyond this land- 

 ing there extends an immense field of mud divided into separate 

 masses in front of St. Trojan, unfrequented and inaccessible from 



