BATHYAL DEPOSITS 673 



shallower water sufficiently removed from the shore to prevent ex- 

 cessive detrital deposition. 



The secondary origin, through erosion of older greensand de- 

 posits and redeposition of the material in shallow water, must also 

 be considered. Such deposits are forming at the present time by 

 the erosion of the Cretacic greensands of the Atlantic coastal plain. 

 Andree (S'SSi) holds that this may have been the origin of green- 

 sand lenses in the Neocomien sandstones of northwest Germany 

 (Teutoburger Wald, especially the Oswing). The lower Cenoma- 

 hien deposits of greensands (Essener Greensand) of northwestern 

 Germany are other examples of such deposits formed near shore, 

 passing laterally near Mons into a shore conglomerate with rich 

 fauna. 



• Greensand is to-day found sporadically on the shallow ocean 

 floor under the Gulf Stream in depths of only a few hundred 

 meters. ( Pourtales-72 : ^p/. ) 



The decomposition of glauconite produces, according to L. 

 Cayeux, ferric hydroxide and pyrite, but other alteration products 

 may also result. Thus the bright-red "Redbank" sands of the New 

 Jersey Cretacic seem to owe their color to the decomposition of the 

 glauconite mingled with the quartz grains of the deposit. This de- 

 composition may be due to the more porous character of these sands, 

 but that it was not produced under present climatic conditions is 

 shown by the bright-red tints which indicate a prolonged period of 

 subjection to dehydrating agencies. 



Deposits on Lee Banks and on the Edge of the Continental Shelf. 



Where ocean currents carrying fine silt pass from shoals to deep 

 water, the checking of the current resulting causes a deposition of 

 more or less of the silt. (Willis-105 : ./p/.) Thus on the lee of a 

 submerged ridge a bank of silt will form, the structure of which is 

 probably that of the delta, the successive additions being at a com- 

 paratively steep angle. The Gulf Stream crosses several shoals or 

 submerged terraces, and deposits of the type mentioned are fonned 

 in the lee of these. "The steepest slope of the Gulf of Mexico from 

 the looth to the 2,000th- fathom line is in the position of a lee-bank 

 northwest of the Yucatan plateau. . . . The Blake plateau, over 

 which the Gulf Stream sweeps north of the Bahamas, is clean, hard 

 limestone, but a lee-bank of mud and ooze is forming on its short, 

 steep slope into deep water." (105:^97.) 



A similar type of deposit is forming on the edge of the conti- 



