180 



AX AMERICAN GEOLOGICAL RAILWAY GUIDE. (VA.) 



1. The term Jurasso-Cretaceous is chosen to designate the Upper Secondary sandstones of the 

 Virginia reports and the associated sands and clays which in their prolongation, northeast through 

 Maryland, Delaware and New Jersey, are found to underlie the Cretaceous green-sand formation 

 of those States, because the fossils found in the vicinity of Fredericksburg, &c., in Virginia, as 

 well as near Baltimore, suggest the upper stage of the Jurassic period; while it is stated that the 

 sands and clays of this belt in New Jersey are referable to the base of the Cretaceous. The whole 

 group would seem in the main to be one of transition, and it is probably best comparable to the 

 European Wealden. 



2. The name Jurasso-Triassic is preferred for the Mid-Secondary rocks of the Virginia reports, 

 as it is thought to correspond best with the fossil indications thus far furnished by the several 

 belts included in it. Of these, the most western area is in part continuous with the so-called 

 Triassic belt of Maryland and Pennsylvania, and in part with the coal bearing rocks of Dan River, 

 North Carolina. The middle belt is in the line of prolongation of the Deep River coal rocks of 

 North Carolina; and the eastern belt, including the Grits and Coal Measures of Chesterfield, 

 Henrico, &c., is topographically without a counterpart. The middle and eastern belts in Virginia, 

 and the western tract in North Carolina, show a close agreement in their fossil flora, which in many 

 particulars has a decidedly Jurassic character, and all three belts are connected by certain species 

 of Estheria, Candona, &c., held in common. Collectively these beds represent most probably a 

 group of deposits ranging through Upper Triassic and Lower Jurassic time, and are in large 

 measure of a transitional character. 



as Cat 



the Trenton period (4 c.), 



these corresponding in limits to the Lower and Upper Silurian periods of the table. 



4. The Middle Cambrian, or Auroral group, occupying much of the surface of the great valley 

 west of the Blue Ridge, and exposed in numerous anticlinals and faults in the mountain belt 

 farther west, is marked by a great preponderance of magnesian limestones in the lower two-thirds 



of its mass, passing below in many cases into Arenaceous and Argillaceous limestones, and fol- 

 ay oolitic and by cherty aud sandy beds, these latter giving place still higher to the 



lowed above by oc 



