THE GREENSANDS OF NEW JERSEY. 1 65 



tion have been oxidized to so great an extent that their separa- 

 tion from the red sands of the Redbank formation is often a dif- 

 ficult matter. 



On account of the great economic importance of the green- 

 sand 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 sec- 

 tions 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. 



Redba7ik 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 Red- 

 bank formation is proposed for the deposits of this horizon. 



The strata are glauconitic throughout, although the great pre- 

 ponderance 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. 



