342 Captain Puillon-Boblaye on the. Tidal and other Zones 



■which demonstrates that the first cause of the phenomenon is 

 independent of gravity. 



The same surfaces present a phenomenon still more interest- 

 ing ; it is that of the numerous grooves rigorously directed 

 according to the lines of the greater declivity. We see them 

 arise upon every culminating ridge^ scooped out and widening 

 as they descend towards the extremity of the inclined plane. 

 The ridges which separate the principal grooves become them- 

 selves the point of the departure of new grooves, which con- 

 verge towards the bottom of the former. We cannot better 

 compare these surfaces than to the plane in relievo of a moun- 

 tainous country. 



The little cavities of from one to two millimetres, which cover 

 all the surfaces, are, in general, a little greater in the bottom of 

 the grooves than on the ridges. Some cavities, much larger 

 than all the others, but yet on a fresh surface, appear disposed 

 upon the lines of fissures, sometimes perpendicular to the direc- 

 tion of the grooves. Finally, and this observation is essential, 

 while the little cavities appear on all the faces, the normal 

 grooves, or those of the greater declivity, are not observed but 

 upon inclined faces ; the horizontal planes are almost entirely 

 without them, and it is almost the same with the vertical planes. 



The immediate cause of the formation of the grooves cannot 

 escape us, for the phenomenon passes under our eyes. Wc see 

 each of them forming itself by the union of cavities situated up- 

 on the same line of the greater declivity. We may affirm that 

 the vicinity of the sea is a necessary circumstance, for the phe- 

 nomenon in actioji presents itself nowhere in the interior of the 

 earth (not even in the vicinity of fresh waters, nor upon high 

 snowy peaks), and as, moreover, its sphere of action does not 

 extend on littoral rocks to more than 40 yards above the level 

 of the sea, and to 1000 or 1500 yards distance from the shore. 

 We can have little doubt, as shewn by these circumstances, that 

 the aura mai-itima, or the particles of the tide carried by the 

 wind, could have been the first cause of the phenomenon ; that 

 they act mechanically by absorption and crystallization, in the 

 manner of concentrated saline solutions upon the frozen rocks, 

 and, besides liygrometrically, by fixing humidity in the parts 

 which they penetrate. Cavities are thus formed on all the faces, 



