388 EHREXFELD— JOINTING AS A FUNDAMENTAL FACTOR 



repeating patterns may be carried out here into the idea of marine 

 planation to reduce the land surface below the ordinary base level. 



This, I take it, is another way of stating one of the points of 

 Barren's paper, referred to above, that in the plains adjacent to 

 the New England coast upstanding structures such as the " ^Monad- 

 nocks " of authors, may be regarded, as the towers and figures re- 

 ferred to off the coast of Spitzbergen, as indicating outlines of 

 marine planation. 



I hope to discuss in a later paper some further details of this in 

 regard to some structures about Portsmouth Harbor. 



The relationship of marine planation to what has been developed 

 as the theory of peneplains is thus a very far reaching problem. 

 That the known action of the sea to wear away the land mass has 

 been underestimated and neglected is perhaps due to the fact that 

 no constant or nearly constant factor to hasten marine degrada- 

 tion has been taken into consideration. The reasoning of some of 

 the older authors would seem to have been based upon the things 

 which are to be observed only as results of local storms and also 

 fails to consider the possible factor of the nature of the litho- 

 sphere itself as an active contributing cause in hastening the reduc- 

 tion of the land mass. 



Some very interesting discussion of the arguments pro and 

 con of marine denudation or degradation may be found in the 

 various editions of A. Geikie's well-known " Textbook of Geology." 

 Thus (3d ed., rev., p. 448) Geikie says: 



" But were it not for the potent influence of subaerial decay, the progress 

 of the sea would be comparatively feeble. The very blocks of stone which 

 give the waves so much of their efficacy as abrading agents, are in great 

 measure furnished to them by the action of the meteoric agents." 



Taken in connection with the more recent studies in jointing as 

 controlling rock disintegration, and in connection with what may be 

 seen along the continental borders both land and marine the above 

 statements will be seen to be an incomplete statement of the factors 

 in the case. 



That entire continental masses may not be seen to have been 

 reduced by this marine planation should not prejudice the case, it 

 is exceedingly improbable that any one agent alone has ever re- 



