SUCCESSIONS OF DEPOSITION. 49 



energy, especially where the tides are high, the erosion, even in a brief period 

 of geological time, is often very great. Thus on the coast of Yorkshire, north 

 and south of Whitby, the marine cliffs, apparently formed in the brief 

 period during which the sea along that coast has had its present attitude, 

 have an average height of several hundred feet, and the platform which 

 marks the lower range of wave action extends on the average a mile or 

 more from the shore. The prism of rock removed by this cutting is in 

 mass greater than we can well assume to have been eroded from the land dur- 

 ing the same period for the distance of 20 or 30 miles from the coast line. 

 Along the shore of New England, though the coast generally lies against 

 rocks of more than usual hardness, the benching action of the sea is almost 

 always noticeable. In the few thousand years during which this coast line 

 has remained at its present attitude, the amount of erosion has apparently 

 been many times as great as over any equally extensive interior portion of 

 the field subject to the action of atmospheric agents. Considering only the 

 hard rocks, especially those of the coast of Maine, I am of the opinion that 

 the atmospheric erosion accomplished in New England since the Glacial 

 period has not been so great as that effected along the shore belt in the 

 much shorter time which has elapsed since those coasts began to be assaulted 

 by the sea. 



It is to be observed that, in all estimates as to the relative value of 

 marine and atmospheric erosion, account must be taken of the dissolving 

 action of the land waters, which is always wanting in the case of the sea. 

 Although the interior erosion of New England is now exceedingly small, 

 the solutional decay is gradually, indeed it may be said somewhat rapidly, 

 advancing in certain portions of the glacial deposits, so that the time will 

 come when they may pass off with greater rapidity. Making allowance for 

 this and for other evident qualifications as to the relative value of marine 

 and interior erosion, it may still be said that the former agent has a certain 

 and important, though much neglected, influence in determining the shape 

 of the lower-lying portions of the land mass. 



CYCLES OF DEPOSITION. 



Considerations as to the succession of phenomena of deposition which 

 were brought into view by the writings of the late Prof. John S. Newberry 

 and others, appear to receive no support from the successions of strata in 



mon xxxiii 4 



