46 GEOLOGY OF THE NARRAGANSETT BASIN. 



does not exceed in volume that which is accomplished by all the rivers 

 which empty into the sea along this part of the shore. We may say, indeed, 

 that the evidence, when fairly considered, leads us to the conclusion that 

 the destruction of the reliefs in the Atlantic coast mountains — the East 

 Appalachians, as we have termed them — has been in a large measure due 

 to the long-continued action of the sea on the zone in which they he. 



In the case of the Narragansett Basin it seems impossible to account 

 for the destruction of the original reliefs by the action of water on its way 

 to the sea. If we take account of the existing water-filled troughs, the arms 

 of the sea, and the rivers, we find a plain cut by relatively wide and shal- 

 low canyons, which are now to a great extent filled with drift. This plain 

 is underlain by rocks of very diverse hardness, so that if its surface were 

 due to the result of the downwearing action of streams it should be most 

 irregularly carved, in place of having that shorn-off aspect which the 

 horizontally delivered stroke of the waves produces. Therefore we may 

 conclude that the difference between the reliefs of the East and the West 

 Appalachians requires us to consider the benching action of the sea along with 

 the base-leveling process effected by rivers. Undoubtedly this latter base- 

 leveling action has to be reckoned, but only as one, possibly the least, 

 important element in the action. It may be noted, in order to complete 

 this interesting story, that the greater part of the West Appalachians was 

 fully protected against the action of the Atlantic by the rampart of the 

 Blue Ridge. It is a corroboration of the hypothesis that at the southern 

 end of the West Appalachians, where these mountains were exposed to the 

 action of the waves of the Gulf of Mexico probably at least until the end 

 of the Cretaceous or the middle of the Tertiary period, the mountains show 

 a measure of erosive action hardly less than that which is exhibited by the 

 worn-down ridges of the Atlantic seaboard 



Some further consideration of the question as to the wearing down of 

 the rocks of this basin will be found in the next chapter, on the glacial 

 history of the field. 



RECENT CHANGES OF LEVEL. 



It may be well in this connection to note the facts concerning the 

 recent changes of level in the Narragansett Basin. As elsewhere remarked, 

 the evidence goes to show that the amount of glacial wearing, or at least 



