822 HISTORICAL GEOLOGY. 



also on Staten Island. It includes tlie clay-beds of northern Long Island, 

 which are well displayed at Glen Cove, and at various points between this 

 place and Huntington and farther to the eastward ; and also part of the 

 clays of Fisher Island, Block Island, and Martha's Vineyard. Gay Head, 

 the west cape of Martha's Vineyard, owes its name to the variously colored 

 clay-beds. 



The several beds of greensand, or marZ, consist of common sand and black- 

 ish to olive-green grains of glauconite — a silicate of iron and potash made 

 chemically within the cavities of the shells of Rhizopods, Corals, and other 

 marine organic materials. The bluffs after a rain often look black or green- 

 ish black. They are called marl-beds because the material is useful as a 

 fertilizer. The fertilizing properties of the marl, according to G. H. Cook, 

 are not due to the potash of the glauconite, but to the presence of some 

 lime phosphate. 



The fresh-water origin of the New Jersey clay-beds is generally recog- 

 nized. The absence of lamination and the thickness indicate, not river action, 

 but the existence of quiet fresh-water areas parallel with the New Jersey 

 seacoast and that of southern New England from New Jersey eastward as 

 far as Cape Cod, or about 300 miles. The coast-line may have been some 

 miles distant to seaward. Rivers were not the transporters, for they do only 

 coarser work. No river in New England, where feldspathic rocks abound, is 

 now making such non-laminated elay-beds. Only small streamlets and rills 

 could have been concerned ; and the feldspathic rocks must have been near 

 by. Eor New Jersey the Triassic granitic sandstones may have been the 

 feldspathic rocks at hand; and for Long Island and the islands to the east- 

 ward crystalline rocks were not far away to the northward. The bleaching 

 of the deposits in the case of the white clay-beds required the action of 

 carbonic acid or organic acids proceeding from the decomposition of beds 

 of peat or leaves underlying the Raritan or intercalated with its layers ; 

 for the clays from granitic rocks always derive a tinge of iron oxide from 

 the black mica and other iron-bearing minerals among their constituents. 

 The origin of the clay-beds in all these particulars was very much like that 

 of those of the coal-formation (page 665). 



After the making of the Raritan beds, the sea regained access, as the 

 marine shells evince, to the shore region of the Atlantic border ; and this 

 was the first submergence of the border since the close of the Lower 

 Silurian. The geanticline, which was probably increasing through the 

 Paleozoic, at last had disappeared. 



The beds of greensand are supposed to have been formed in moderately 

 deep waters off the coast. The least depth required for the production of 

 greensand is not known. 



Ehrenberg, who first discovered that the grains of glauconite often have the shape of 

 casts of Ehizopod shells, also detected them in the hones of the Zeuglodon of the Ala- 

 bama Tertiary, which were probably in shallow water when the formation took place. 

 J. W. Bailey reported in 1856 their occurrence in the cells of recent Corals and Rhizopods, 



