348 MINERALOGY OF THE REDHEAD. 



tides. The floors of many of these caves being 

 elevated above high- water mark, have led some to 

 infer a rising of the land or a depression of the 

 level of the sea, subsequent to the period of their 

 formation, — suppositions equally gratuitous and 

 unnecessary. If a small cavity is once formed in 

 the soft sandstone, (and caves are always situated 

 in the softer parts of the strata), within the reach 

 of the tide, it will speedily be hollowed out into 

 a cave by the action of the surge, and this cavity 

 will increase in length and height more rapidly 

 than in breadth and depth. The innermost part 

 offering the greatest resistance, will be assailed 

 most violently by the force of the sea ; and the 

 floor will acquire an inclination, rising as the cave 

 increases in length, in consequence of the direc- 

 tion given to the progressive motion of the littoral 

 waves by the sloping position of the shore. During 

 a storm, the external opening will act like a funnel, 

 and conduct each billow, with its ascending motion, 

 to spend its destructive force in the farthest part of 

 the cave, and there scoop out a recess greatly be- 

 yond the reach of an ordinary tide. If the out- 

 works of this recess arc removed by the action of 

 the sea, a cave will then open to-day, with its floor 

 higher than the present level of the ocean. There 

 are many caves both on the east and west coasts of 

 Scotland, which have formerly been excavated by 

 the action of sea, but whose pavements at present 

 are never washed by the tide. These, in all pro^ 



