170 THE JOURNAL OF GEOLOGY. 



then within circumscribed limits, which are constantly subject to 

 modification, is the production of greensand possible. 



GENESIS OF THE DEPOSITS. 



The opening of the Cretaceous period along the Atlantic 

 border witnessed the deposition of large amounts of irregularly 

 stratified sands and clays together with beds of gravel in the 

 vicinity of the coasts. It was a period of great mechanical dis- 

 turbance over the area of deposition, and both the physical and 

 faunal characters of the strata point to the close proximity of 

 land, while enclosed basins doubtless existed for a portion of the 

 time. 



With the opening of the epoch of greensand deposition, as 

 represented in the Matawan formation, much the same condi- 

 tions at first prevailed. Alternating beds of sand and clay were 

 laid down, but gradually the coarser elements disappeared, depo- 

 sition became less rapid and greensand was locally developed. 

 The conditions for greensand production were not widely 

 extended nor long existent, for successive periods of rapid and 

 slow accumulation of materials continued to the close of 

 Matawan deposition. 



With the advent of the Navesink epoch land-derived mate- 

 rials became greatly reduced in volume and shortly ceased 

 almost altogether, so that throughout the area of deposition 

 there was formed at this horizon some forty feet of highly glau- 

 conitic greensand. Toward the close of this period terrigenous 

 deposits became more pronounced, but the production of giau- 

 conite did not altogether cease. 



With the opening of the next epoch, represented by the Red- 

 bank formation, dark sands in which the proportion of glauconite 

 was very small were at first deposited. Throughout the whole 

 series of beds glauconite is found distributed in greater or less 

 amounts, but at no time did its production reach the prominence 

 that it had during the previous epoch. The marked admixture 

 of coarse elements throughout most of the deposits rendered 

 them later subject to the ready percolation of water by which 



