UPPER SECONDARY ROCKS. 



257 



CHAPTER XXIII. 

 GEOLOGY OF THE UNITED STATES. 



UPPER SECONDARY FORMATIONS. 



(Supermedial Order. Cretaceous, Oolitic, and Sand- 

 stone Groups. — De la Beche. Saliferous System.) 



Upper Secondary. — Division. — How Distinguished from Ter- 

 tiary. — New Red Sandstone. — What it Includes. — Its Range 

 and Extent,— Oolite.— Green Sand. — Equivalent to Cretace- 

 ous Group. — Its Fossils. — Its Range and Extent. — Mode of 

 its Formation. — ^General Results. 



The rocks of this formation, we have already 

 stated, are divided into four groups, viz. : 



1. Cretaceous or Chalk. [ 3. Green Sand. 



2, Oolitic. I 4. New Red Sandstone. 



This group of strata is easily distinguished from 

 those of the tertiary, not only by their chemical 

 character and greater compactness in their mechan- 

 ical structure, but also by a marked difference in 

 their organic remains, and by a want of conformity 

 in this strata, as they are rarely parallel to those of 

 the tertiary, and also exhibit greater evidence of 

 having been disturbed and changed from their ori- 

 ginal position. The organic remains in this forma- 

 tion are also mostly petrified ; in the tertiary they 

 generally are not. The first three of the series are 

 evidently of marine formation. 



New Red Sandstone. — According to our arrange- 

 ment, proceeding upward, we find, next to the mill- 

 stone grit, the new red sandstone, so called because 



