Dana and Chambers on Ancient Sea- Margins. 217 



river will tell the tale as well as the beach along the coast, 

 — if so, the terraces described by Chambers as occurring 

 over these upper regions, cannot all be proofs that the sea 

 there left beaches ; and it remains for investigation to esta- 

 blish, by other evidence than the mere existence of such 

 *' benches" or " shelves" of land, that any are of that origin. 

 Indeed, the whole work, as far as the subject bears upon the 

 question of elevation, remains yet to be done, excepting the 

 observations relating to the exterior of the island. If there 

 have been elevations of the land corresponding to the sea- 

 shore terraces of 20, 32, 66, 64, 117, 126, 188 feet, there 

 must, for the reasons stated, be traces of river-terraces high 

 up on the land, corresponding to each elevation, making a 

 most complex problem for investigation to unravel. These 

 facts have led to our separating the sea-shore terraces from 

 the others, in the Table given on a preceding page. 



8. Another consideration comes in, complicating still more 

 the problem. Suppose the coast to be raised independently 

 of the country back, or to a greater height. This is a pos- 

 sible case, and should be a matter of investigation. It is ob- 

 vious, that the river excavations would be confined to the 

 parts toward their mouths, and here the terraces would be 

 found. At certain places, the slope of the river's bed would 

 be diminished instead of increased ; and in such parts the 

 water would be set back ; its bed would fill up ; its flats 

 would be flooded more frequently than before, or perhaps 

 constantly, and they would consequently increase in height 

 by new accumulations. Near the sea, — in such a case, the 

 river-terraces might slope vath the bed of the stream, while 

 in other places they would be absolutely horizontal, and 

 higher up the valley be wanting altogether. 



9. One important conclusion, obvious without farther re- 

 mark, is, that the terraces in the higher portions of a coun- 

 try are not satisfactory evidences of as many distinct eleva- 

 tions, nor of the actual height of any elevations the country 

 may have experienced. The teri'aces toward the sea are 

 more trustworthy. 



There is a certain rule in the examination of rock deposits 

 — well understood and generally applied — which is entirely 



