Page:The Journal of geology (IA journalofgeology21894univers).pdf/179

tion have been oxidized to so great an extent that their separation from the red sands of the Redbank formation is often a difficult matter.

On account of the great economic importance of the greensand beds of the Navesink formation frequent pits have been dug into it all along its line of outcrop from the northern to the southern end of the district. As a result the strata may be studied to great advantage.

A magnificent exposure is found in the great bluffs of the Navesink Highlands facing the Raritan Bay, while excellent sections are to be found along many of the streams that cut through the formation. The beds are highly fossiliferous and the most varied fauna in the New Jersey Cretaceous is found at this horizon. Between 300 and 400 species have been described.

The Navesink formation has a pretty constant thickness of 40 feet, although locally ranging from 30 to 60 feet. The deposits have been found to be remarkably persistent in character both along the strike and dip, so far as they have been examined.

Redbank formation (Red Sand).—The bright red sands of this formation afford one of the most striking features of the country throughout the marl district. They are extensively developed in the vicinity of Redbank, and on that account the name Redbank formation is proposed for the deposits of this horizon.

The strata are glauconitic throughout, although the great preponderance of coarse arenaceous sediments has facilitated the oxidation of the greensand, changing the green color of the beds to red or brown. The lower portion of the Redbank formation is often composed of black sand or sandy clay, while at the top of the formation there is an indurated clayey layer generally of a distinctly greenish color. This hardened stratum has had an important influence in the development of the topography of the marl district, and especially in the extreme north the higher hills are largely due to its presence. The fossils are in the main the same as in the preceding formations, but on account of their poor preservation have not up to the present time been very fully studied. The indurated layers have afforded the greater number.