14 CRETACEOUS GROUP 
With respect to the basis on which the ferruginous 
sand rests, I know nothing with certainty; for although 
the strata have been penetrated nearly one hundred feet 
at the Chesapeake and Delaware canal, they afford no an- 
swer to this question. But I am disposed to believe that 
in the northern states this formation rests on primitive 
rocks, and in the southern states, especially in Alabama, 
on the old secondary limestone. The latter opinion has 
recently been much corroborated by the researches of Mr. 
Conrad. If hereafter it should be proved that the northern 
section of our cretaceous group rests upon primitive rocks, 
as just suggested, it will be similarly circumstanced to the 
same formation in Sweden, where, according to Mr. 
Nilsson, the chalk is generally incumbent on gneiss. 
Again, in the Carpathean mountains, the chalk and gra- 
nite are in immediate contact. * 
NEW JERSEY. 
Ferruginous Sand. In New Jersey, the tract which 
has long been known by the name of the “ marl district,” 
may be located as follows :—Draw two lines, one from 
Amboy to Trenton, the other from Deal to Salem ; let 
the Atlantic ocean connect the eastern, and the Delaware 
river the western points of these lines: this irregular ob- 
Jong tract incloses nearly the whole marl deposit of 
New Jersey; so far, at least, as it has hitherto been ex- 
plored. There is reason, however, to suppose that it 
occupies a much larger proportion of the peninsula, espe- 
* De la Beche, Geol. Man. pp. 256. 
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