Page:The Journal of geology (IA journalofgeology21894univers).pdf/184

then within circumscribed limits, which are constantly subject to modification, is the production of greensand possible.

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 disturbance 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 conditions at first prevailed. Alternating beds of sand and clay were laid down, but gradually the coarser elements disappeared, deposition 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 materials 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 glauconitic greensand. Toward the close of this period terrigenous deposits became more pronounced, but the production of glauconite did not altogether cease.

With the opening of the next epoch, represented by the Redbank 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