CHAPTER IX 



RECONSTRUCTIVE PROCESSES — MARINE AND ESTUARINE 

 DEPOSITS 



VI. Marine Deposits 



The sea is the great theatre of sedimentary accumulation, and 

 rocks of marine origin form by far the largest part of the present 

 land surfaces. Important as other classes of deposits may be, all 

 of them together are very much less so than those laid down in 

 the ocean and the waters immediately connected with it. There 

 is great variety in the sedimentary deposits made in the sea, which 

 change in accordance with the depth of water, the nature of the 

 coast rocks, the force of winds and tides, and the nearness or 

 remoteness of the mouths of rivers. Large land-locked seas, like 

 the Gulf of Mexico and the Mediterranean, again, have deposits 

 more or less different from those of the open ocean, a difference 

 which is largely due to the absence or insignificance of the tide, 

 and the reduced force of the waves. 



It is important to remember that the actual line of meeting of 

 sea and land is not the structural margin of the continent, for the 

 water may cover a broad submerged shelf of the latter. For ioo 

 miles east from the coast of New Jersey the water deepens very 

 gradually to the ioo-fathom line, whence it shelves very steeply 

 to the profound oceanic abyss. The ioo-fathom line, which may 

 be far out, or close inshore, generally represents the true margin 

 of the continental platform. (See Fig. 63.) 



Marine deposits may be classified primarily in accordance with 

 the depth of water in which they were laid down, one of the most 

 valuable guides to the history of ancient rocks, and secondarily in 

 accordance with the nature of the material of which they are com- 



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