Page:The Journal of geology (IA journalofgeology21894univers).pdf/191

more constant, although there were times when it became greatly reduced in amount on account of the advent of large amounts of sand and mud from the adjacent coasts.

From the known conditions requisite for the production of glauconite upon the bed of existing seas, and the possible position of the coast line in Cretaceous time, it seems likely that the greensands now outcropping at the surface were laid down from fifteen to thirty miles off the coast. Frequent changes of level no doubt took place, but the variations in the character of the deposits were probably quite as much due to fluctuations in the currents as to pronounced changes in the position of the coast line.

The marked thickening of the Matawan formation seaward, as shown by the well-boring at Asbury Park, is of interest as indicating the more permanent character of the deposition outside the area of mechanical disturbance such as characterized the shallower portions of the Matawan sea floor.

The alterations which have taken place in the exposed portions of the deposits are oftentimes widespread, and in the case of the indurated layers at the top of the Redbank formation have determined to a large extent the topography of the greensand district.

Many interesting problems are presented for further study, but it is hoped that this paper may contribute somewhat to a clearer understanding of greensand deposits in general, and those of the New Jersey area in particular.