52 FOURTH REPORT — 1834. 



" A white soft limestone, not harder than some coarse chalks, 

 which it much resembles, replete with fossils. 



" All these varieties occasionally contain infiltrations of sili- 

 ceous matter, and considerable masses of chert are sometimes 

 observed in them : they also present some appearances of the 

 green grains so characteristic of the marls adjacent." 



These calcareous strata appear to be much less abundantly 

 distributed in New Jersey than the friable sands and marls upon 

 which they rest, for they have hitherto been found only at in- 

 terrupted intervals along the south-eastern border of the marl 

 region. 



Limestone strata, however, seem to compose nearly the whole 

 of the cretaceous group in the Southern States, where they exist 

 on a scale of vast extent and thickness, rising into bold undu- 

 lating hills, which resemble in their features the surface of the 

 chalk in Europe, and seldom or never repose upon the sands 

 which form their substrata in New Jersey. In Alabama, Mr. 

 Coni-ad states this formation to constitute nearly the whole bed 

 of the country, the eocene occupying very limited patches in 

 the valleys of some of the rivers. Generally throughout Georgia 

 and the States south and west of it, these limestones are deve- 

 loped as two distinct strata. That which is universally superior 

 in position is a very white friable limestone, containing many 

 casts of shells peculiar to itself, while beneath this is a compact 

 blueish limestone, alternating with friable limestone and with 

 greenish siliceous sand, which is indurated into a rock, and con- 

 tains fossils and the peculiar green particles of silicate of iron. 

 The thickness of the lower deposit is stated to be about 300 feet 

 on the Alabama river. Its characteristic fossil is the Exogyra 

 costata, the same shell which is so remarkably distinctive of the 

 marl beds in the ferruginous sand formation of New Jersey and 

 Delaware. 



In some places, as in Wilcox county, Alabama, this lower 

 limestone is seen to rest upon a still inferior bed of a friable 

 greenish sandstone, containing fossils, especially the Ostrca fal- 

 cata, and also presenting, like the limestone above it, some of 

 the green grains everywhei*e characteristic of these cretaceous 

 formations. 



Ferruginous Sands of New Jersey . — These arenaceous strata 

 compose tne chief mass of the secondary deposits in New Jersey, 

 being buc partially overlaid by the very thin calcareous strata 

 before mentioned. The mineralogical character of this deposit 

 is extremely variable, though the most usual constituents are 

 the following : 1st. Siliceous sand, mostly yellowish and ferru- 

 ginous, though sometimes cf a green colour, answering to the 



