RED-SANDSTONE DIVISION. 
285 
define the geological era of the trappean rocks, can easily be ascertained by those who are 
favorably located to make the proper observations on Long and Staten islands. It is consi¬ 
dered highly probable, from the imperfect observations I have made on this subject, that the 
trappean rocks were formed at the epoch of the marl and green marl deposits of New-Jersey. 
III. RED-SANDSTONE DIVISION. 
This division of rocks occurs in the First geologicial district, in Rockland and Richmond 
counties, associated with and underlying the trappean rocks that have been described. These 
are parts of the great formation of red sandstone, stretching from Stony point in Rockland 
county on the north, through New-Jersey, Pennsylvania, Maryland, Virginia, into North- 
Carolina on the south. 
In Richmond county (Staten island), the red sandstone occupies but a small area where it 
can be observed; but from the observations made by Prof. H. D. Rodgers and myself, it is 
believed to range from between Bergen point and Shooter’s island, south-southwestwardly, to 
the Freshkill marshes. It is generally covered by soil, drift deposits, and the sand and clay 
beds. It may be seen at very low tide, on the shore, about southwest of Bergen point. It is 
the slaty, micaceous, fissile, red sandstone and shale. 
The red-sandstone region of Rockland county is a fine agricultural district. The land is in 
some parts much broken and stony, but in general it is rolling, with a rich sandy loam, re¬ 
sulting from the disintegration of the subjacent sandstone and its associated shales, marls and 
limestones. The strata are in general slightly inclined one to three degrees to the westward; 
but near the granitic rocks, near Grassy point, they dip southwardly at a considerable angle, 
ranging from fifteen to forty-five degrees. This rock occupies that portion of Rockland county 
from Grassy point along the base of the Highlands to New-Jersey, and eastward to the Hud¬ 
son river, but a portion of its area is covered over by trap rocks. In color, it varies from 
chocolate-brown, through brick-red and grey to white ; in texture, it varies from pebbly con¬ 
glomerate, through common sandstone, fissile and micaceous sandstone, to shale ; and in com¬ 
position, from perfectly siliceous, to an argillo-calcareous marl. Where the trappean rocks 
have cut through these various strata, or have spread laterally between them, their texture and 
appearance are much modified, and appear to have been subjected to the action of heat, which 
has partially melted them, or rendered them more compact and hard, like a hard burnt brick, 
or has made them metalliferous.* 
The useful varieties of this rock are the grey and red conglomerate sandstone, which is 
used for the hearths of iron furnaces ; and the red sandstone, ox freestone, so extensively used 
* Micaceous oxide of iron in small brilliant scales, is not uncommonly diffused thuough these strata near their junction with trap. 
