20 FOURTH REPORT 1834. 



is derived from the violent disintegration of a much more ancient 

 formation than that in which it occurs, namely, of a cretaceous 

 deposit, like that of New Jersey, which may possibly underlie 

 this island and Long Island also, they being exactly in its range. 

 The dip and contortion of the strata at Gay's Head lend consi- 

 derable probability to the foregoing explanation of the origin of 

 this bed of detritus from the greensand. In other quarters, the 

 ancient alluvial beds which I am discussing are usually nearly 

 horizontal, or when they incline, it is with a gentle dip towards 

 the ocean ; but in the strata at Martha's Vineyard the dip is 

 abrupt and in the contrary direction, being to the north. These 

 circumstances, taken in conjunction with the fact, that a pre- 

 cisely similar deposit of detritus from the greensand formation 

 covers the northern edge of that group of beds in many spots in 

 New Jersey, where I have seen it not far east of the beds of 

 so-called plastic clay and lignite, — as, for example, between New 

 Egypt and Bordentown, — make me venture to put forward the 

 suggestion that the cretaceous formations of our coast have 

 probably extended further to the north-east than at present, oc- 

 cupying what is now Long Island Soimd, and its prolongation 

 eastward. Viewing the island of Martha's Vineyard and Long 

 Island as remnants of a more extensive ancient tract in structure, 

 like the peninsula of New Jersey, we can readily account, I 

 think, for all the above phaenomena, together with some others 

 which they present. 



According to Hitchcock, similar strata of the tertiary clays, 

 which I have called ancient alluvium, underlie the diluvial 

 covering in both Nantucket and Long Island. They are con- 

 spicuously exposed in New Jersey, in the sections of the rail- 

 road near Amboy, and again very strikinglj' on the Delaware, 

 near Bordentown. Here they have all the features which they 

 display at Martha's Vineyard, with the exception that they are 

 nearly horizontal and less brightly variegated in colour. Lignite, 

 containing pyrites, dicotyledonous M'ood, and amber, abound in 

 the dark tenacious clay or ancient peat, which has here a thick- 

 ness of many feet. The following description of this formation 

 in New Jersey and the States south of it will serve to show its 

 extensive range and important character. 



In ascending the Raritan it is traced on the south-east shore 

 to within three miles of Brunswick. Approaching Bordentown 

 by the rail-road it is conspicuously exposed for several miles 

 in nearly all the deep cuttings. At Bordentowii the banks of 

 the Delaware consist of its various beds of brilliant sands and 

 dark and white clays for more than two miles. At Philadelphia 

 it occurs, but at a lower level, remains of trees having been 



