260 OOLITIC. — GREEN SAND, ETC. 



which we shall refer to this system, extending from 

 the Potomac River, near the 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 

 fine-grained and compact, forming a good building- 

 stone, for which it has been employed for public 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, 

 Schoharie, Easton (Pa.), Franklin (N. J.), but they 

 are not regarded as equivalents to the European 

 oolite, either in respect to position or organic re- 

 mains. 



Green Sand and Cretaceous Groups. 



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 



