RIPPLE MARKS EPRY. 309 



to collect periwinkles. The water, consequently, is receding. One, 

 however, perceives no trace of its having covered the sands. Their 

 remarkably smooth, wet surface has the polish and the gleam of a 

 mirror. 



In contrast, in many places, especially near the time of the very 

 low water of the spring tides — for example, on the bars that form 

 at the mouth and along the banks of certain rivers — ^ripple marks are 

 found, which, unlike those shown in figure 1, are not a few centi- 

 meters high, but 50 to 75 centimeters, or even a meter. Such ripple 

 marks are shown in figure 7, from a photograph taken at the mouth 

 of the Steir,^ or lagoon of Lesconil. 



As the ripple marks, then, do not form on the upper part of the 

 beach, but are extremely common on the lower part (which corre- 

 sponds in sandy regions to the zone of fucus and laminarian sea- 

 weeds of rocky shores) does it not seem that it ought to suffice, in 

 order to discover their origin, to note the points in which the latter 

 diilers from the former? This reasoning is correct, and it is pos- 

 sible to draw important conclusions from this comparison. From 

 this point of view, however, it is of importance to proceed in one's 

 deductions with a prudent circumspection, without taking one's eyes 

 from the facts; otherwise, one is in much danger in a moment of 

 inattention of arriving at an explanation of the phenomenon, which, 

 when pursued a little further, will very quickly surprise one by be- 

 coming in complete discord with all the new data acquired by 

 observation. 



What, then, is the principal difference between the two parts of 

 the beach, from the particular point of view which we are taking? 

 The slope of the lower beach is much more gentle, so gentle at times 

 that the waves in certain regions recede for a distance of several kilo- 

 meters in attaining the level of low water. Consequently, the velocity 

 of the current of the tide is there very great. In the Bay of Mont- 

 St. Michel it is equal to that of a horse galloping. On the other hand, 

 throughout the duration of the flowing tide, the progressing stratum 

 of water which moves up the sands is very thin, so thin, indeed, that 

 the waves can not perpetuate themselves and die out at a considerable 

 distance from the shore. These beaches are, while they last, like 

 immense shallow lakes which gradually empty themselves. What is 

 one to conclude from such a state of things ? Given the slight thick- 

 ness of the layer of water, it seems quite natural to believe that the 

 action of the wind should make itself felt at the bottom, fonning 

 there ridges analogous to those which it raises on the surface of the 

 sea. One may equally be led to inquire whether it is not necessary 



^ The Steir is a little Breton river, which empties into the Odet at Quimper. But in 

 that region they designate thus most of the small creeks without name that toward the 

 ocean spread out into fjords, estuaries, or lagoons. 



