498 THE JOURNAL OF GEOLOGY. 



composed of sands which are indeed fine near the eastern edge, 

 yet are distinctly granular and incoherent. But soundings on 

 the steep slope beyond the IOO fathom line have brought up 

 very fine silt from the bank of which that slope is the surface, 

 and this silt passes at its foot into globigerina ooze. The zone 

 of transition from clean sand to silt is as sharp as the edge of 

 the slope and is coincident with it. It is evident that the sus- 

 pended mud which escapes beyond the estuaries and sounds of 

 the littoral is swept out until the undertow expands over the edge 

 of the escarpment, and is diffused in deep water ; there the silt 

 forms a great bank 1 0,000 feet high, with a slope of 3 to 8 

 degrees, which has grown seaward during geological ages, and 

 continues to expand as erosion continues on the land. 



The structure of this deposit can only be inferred, but it is 

 worthy of consideration. The surface of accumulation, to which 

 bedding planes are probably parallel, is inclined at a considerable 

 angle, and traverses the bank from top to bottom obliquely to 

 the vertical thickness. The direction of the growth is outward, 

 not upward. The conditions of deposition are similar to those 

 of a delta advancing into fresh water, and the structure of the 

 deposit is probably similar to that shown by Gilbert for a fresh- 

 water delta. (Fig. 14, p. 68, Lake Bonneville). If the detritus 

 was sand, instead of silt, the conditions would be identical, and 

 the bedding which would be exposed by removal of the hori- 

 zontal upper layers would represent an enormous thickness of 

 strata, inclined at a dip corresponding to the slope of the bank. 

 Russell rejects explanations of the attitude of the Newark beds 

 so far as they are founded on sedimentation, 1 but it seems possi- 

 ble that they may present the structure of lee banks. It may 

 also be probable that isoclinal structure, where repetition of strata 

 does not occur, is evidence of this form of deposition and of the 

 conditions essential to it. 



Deposits of this character, consisting usually of clay or silt, 

 are significant of extended rock decay on the land, of currents 



1 Bull. U. S. G. S. No. 85, Correlation Papers.— The Newark System, p. 78. I. 

 C. Russell. 



