Page:The Journal of geology (IA journalofgeology21894univers).pdf/181

centage of soluble phosphates in the Manasquan marl has long given it a high reputation as a fertilizer.

The thickness of the strata has been estimated at 65 feet.

Shark River formation (Upper portion of the Upper Marl Bed).—The term Shark River Marl was earlier employed by the writer to embrace the "blue marl" of the Upper Marl Bed, which has been generally referred in recent years to the Eocene, although the beds are conformable with the underlying strata concerning whose Cretaceous age there is apparent unanimity of opinion.

The Shark River formation is a characteristic greensand with a slight admixture of argillaceous materials, while a hardened and stony layer is found directly at the top. The fossils are numerous, but cannot be readily compared with those from the Eocene areas to the southward. The strata of the Shark River formation have not been found at any point to exceed 12 feet in thickness.

The Shark River formation closes the series of greensand deposits. It is unconformably overlain by strata of a very different character which show evidence of marked mechanical disturbances and rapid deposition.

Throughout the entire sequence of deposits just described, the presence of greensand has been the most distinguishing feature. Its origin is therefore a matter of great importance to the understanding of the several formations, and will be briefly discussed.

Greensand has been found in greater or less amounts at nearly every geological horizon, from the Cambrian down to the present time. It is not an original deposit of clastic origin, but secondary in character. An examination into the conditions of production which surround those deposits forming upon the floor of existing seas will afford an explanation of the strata of past geological time.

Great light has been thrown upon this subject as a result of he deep-sea dredgings which have been made in recent years