260 OOLITIC. — GREEN SAND, ETC. I 
which we shall refer to this system, extending from j 
the Potomac River, near tho mouth of Occoquan, in 
a direction a little west of south, to the Rappahan- 
nock, and thence south across the State of Vir- ' 
ginia. It occupies a narrow belt, in some places 
only a few miles wide, resting upon the eastern 
edge of the primary region, as it does in New-Jer- 
sey, and disappears beneath the tertiary beds of the 
Atlantic plains. It is called freestone, and often is j 
fine-grained and compact, forming a good building- ' 
stone, for which it has been employed for pubhc ed- 
ifices in Washington City. Its fossils are exclu- 
sively vegetable, and of entirely different species 
from those which characterize the coal formations. ] 
The nature of the fossil remains would seem to 
refer the above rock to the period of the oolite 
group of Europe, but we choose to consider it as 
the upper series of the new red sandstone formation. 
Oolitic. 
The next division of the upper secondary rocks 
is the oolitic. Limestone rocks, having an oolitic 
structure, have been found in several places in the 
United States, as at Warwick (N. Y.), Saratoga, i 
Schoharie, Easton (Pa.), FrankUn (N. J.), but they i 
are not regarded as equivalents to the European | 
oolite, either in respect to position or organic re- 
mains. 
Green Sand and Ci^etaceous Groups, j 
The next group in this ascending series is the ' 
green sand, which forms a belt on which the tertia- 
ry rests, extending from Sandy Hook to Georgia. 
With this, however, we shall describe the strata of ! 
the cretaceous period, so called, as it seems impossi- 
ble to separate them. The true chalk has never been 
discovered in this country ; yet, from the character 
of the fossil remains, some of our best geologists 
