DYNAMICAL GEOLOGY. 



England, at depths between 300 and 550 feer, from a region southeast of Montauk 

 Point to that southeast of Cape Henlopen, the soundings, according to Bailey (Smith- 

 sonian Contrib., ii., and Am. J. Sci., II. xvii 176, xxii. 282), consist chiefly of these 

 shells. At greater depths, beyond the limit of the plateau, Pourtales found almost a 

 pure floor of Rhizopods (Trans. Amer. Assoc, for 1850, 84, and Rep. Coast Survey for 

 1853 and 1858); and the facts have been confirmed by later investigation. The species 

 are deep-water forms, differing thus from those of the New Jersey Cretaceous beds. 

 Pourtales observes, in a letter to Professor Bache (dated May 17, 1862), that, along the 

 plateau between the mouth of the Mississippi and Key West, for two hundred and fifty 

 miles from the mouth, the bottom consists of clay, with some sand and but few Rhizo- 

 pods ; but, beyond this, the soundings brought up either Rhizopod shells alone, or these 

 mixed with coral sand, Nullipores, and other calcareous organisms. The Rhizopod 

 shells continue to a depth of 12,000 to 15,000 feet along with other life, as stated on 

 page 611. But beyond this these shells are absent; and since they have reached the 

 bottom elsewhere by dropping from various levels, and largely from near the surface, 

 their absence at these depths is owing to the conditions of the region, and, probably, as 

 Sir Wyville Thomson has suggested, to the solution of them by the carbonic acid 

 present in the waters. The bottom is made for the most part of a red ooze colored by 

 iron sesquioxide, which is supposed by him to be the earthy matter of the same shells, 

 and probably more or less of volcanic ashes (p. 633). Over the bottom in the Pacific 

 black nodules of manganese oxide occur which has been referred, but with a query, to 

 the pyroxene of such ashes. The dissolving away of the coral rock of Bermuda has left 

 a red soil which Thomson considers to have come from the corals, like the red ooze from 

 the Rhizopods, though in each case these ingredients are only very sparingly present. 



4. Action of the Oceanic Waters over a submerged Continent, 

 and during a progressing Submergence or Emergence. 



During a slowly progressing submergence of a continent the waves 

 and marine currents would work over the loose earth, gravel, and allu- 

 vium of the surface for a depth of possibly a hundred feet or so, there- 

 by changing them into marine deposits ; the living species of the land 

 and fresh waters would be destroyed and marine life would be intro- 

 duced ; and the general features of the surface would be changed through 

 a wearing off of heights and a filling of preexisting valleys, and not by 

 the excavation of valleys. It might be supposed, at first thought, that 

 the ocean would wash through the valleys with great excavating force, 

 and make deep gorges over the surface. But from the present action 

 on sea-coasts it is learned that with each foot of submergence, the sea- 

 beach would be set a little farther inland, so that the whole would 

 successively pass through the conditions of a seashore ; and on exist- 

 ing seashores, the action in progress, instead of tending to excavate 

 valleys, is everywhere wearing away exposed headlands, and filling up 

 bays. The salt waters, in fact, enter but a .short distance the river- 

 valleys of a coast, because they are excluded by the out-flowing stream. 

 The bottom of the Hudson is below the sea-level, for a long distance 

 beyond the limit to which the pure ocean-water extends : the same is 

 true of the St. Lawrence, and of many other rivers along the coast. 

 During a progressing submergence, therefore, the ocean would have 

 no power of excavating narrow valleys, unless they happened to be 



