RIPPLE MARKS — EPRY. 311 



junction of the upper and the lower beach. This line of demarkation, 

 sometimes scarcely visible, is remarkably clear in the accompanying 

 illustration (fig. 8). 



Examine this photograph closely and what do we see? A higher 

 beach which is perfectly smooth, a lower beach, almost horizontal, 

 equally leveled off by the sea that has withdrawn from it. Between 

 the two, at the base of the upper slope, are two small pools quite 

 distinctly united, of which the bottom in course of becoming dry is 

 covered with ripple marks. Why are these ridges formed there and 

 not higher up or farther out? 



Let us pursue our examination, concentrating our attention on the 

 nearer depression the details of which are the more distinct. In the 

 widest part of this pool the ridges are arranged parallel with the 

 shore, but at its extremities, situated in the nearest foregi'ound, it is 

 seen that these lines of ridges are directed toward the sea, diminish- 

 ing in number, losing their regularity, and finally mingling together 

 and being drawn out into a little streamlet which gradually disap- 

 pears. If we could study the other pool as readil3^ we should dis- 

 cover an absolutely similar disposition of the ripple marks at the 

 bottom of it. It also terminates in a rill. The two together seen 

 from farther off and higher up from the top of the cliffs (fig. 9) 

 present with perfect symmetry the appearance of a pair of French 

 mustaches with long ends drawn down equally. 



What has gone on here? It should not be imagined that hiero- 

 glyphics are more easy to decipher than these marks traced on the 

 sand. Wherever the strand was so flat that the water could flow 

 normally from the cliffs and toward the sea, the sand}^ grains, what- 

 ever might be the manner in which they were propelled, strike briskly 

 against the waves, or the natural impulse of the tide. Whatever the 

 inclination of the area on which they roll (in other words, whether 

 on the lower beach as on the higher beach, as one can verify from the 

 foregoing photograph), they are deposited in a uniform layer. They 

 can not follow the same covirse in a double depression. Those which 

 at first, when the sea strikes the plain far from the foot of the cliffs, 

 had not the least importance end by acquiring one a little before the 

 receding tide completely abandons them. At this moment the layers 

 of water which sweep the depression from side to side, rise swiftly 

 to a certain height on the slope of the upper beach, but in returning 

 all the water can not again avoid the constantly growing obstacle 

 which extends across its route on the progressively exposed plane 

 of the lower beach. At the surface a part of this water still passes, 

 but the greater portion, diverted by the knob of sand toward the 

 middle of the pool, accumulates there seeking its level of equilibrium, 

 and in order to find it flows out in a wavy course to the right and 



