SHORE CAVES AND ARCHES i; 



the excavation is made in good working order; unless the 

 slope is considerable, the inrushing waves will heap larcre 

 stones in such (quantities against the inner end of the open- 

 ing that the surges cannot move the whole mass, and the 

 bed-rock will be preserved from the blows of the bowlders 

 which then expend their force on each other. 



The result of this steep slope, of the cavern floor is, that 

 if the sea-cliff be low, the extremity of the cavern finally 

 attains the surface, and gives the conditions which produce 

 what in New England is called a '' spouting horn." The 

 waves, in time of heavy storm, rush up the crevice with a 

 speed accelerated by the narrowing of the opening in its 

 inner parts, and send a mass of foam high into the air. 

 Another condition which produces an interesting group of 

 spouting caves is found when the cavern has the top of the 

 portal low, and a considerable space within which has no 

 communication with the outer air except by the opening into 

 which the wave sweeps. Rushing into the cavity, the billow 

 energetically compresses the air until the motion of the water 

 is arrested ; this air then, expanding, blows the water back- 

 ward toward the sea, discharging a good part of it like the 

 smoke from a cannon. This group of caverns is less noted 

 than the spouting horns, for the reason that, though they 

 are the more common, it is rarely possible to see them when 

 the waves are high. It is only when some sharp headland 

 gives a coign of vantage whence we can look down upon 

 a long stretch of cliff shore, that these peculiar features of 

 wave-work can be well observed. 



Another group of shore features sufficiently frequent to 

 deserve notice are the arches and natural bridges. On our 

 New England shore these features are uncommon, tor the 



