598 



MESOZOIC FLORAS OF UNITED STATES. 



t represented 675 feet. 



Stratified sands and clays. cb.iefl\ 

 redeposited from the uaderl\ 

 I ing Rappahannock beds. Fossil 

 plants in the clay seems, large[> 

 dicotyledons. Typical species 

 Sapindopsis variabilis. 



Sand 01 

 quartzitit 



Stratified sands and clays, the 

 former often thick and of fine 

 quality; the latter in thin 

 seams and plant-bearing, otten 

 black and representing forest 

 beds filled with comminuted 

 egetable matter and impure 



. and occasionally ( 



.v'hat pure, cross-bedded samLs 

 with worn quartz and other peb 

 bles, containing beds of dark clay 

 of varying dimei 



Typical species: Dioonil 



e); plant bearing (cycads): 

 Athrotaxopsis exjiansa, Clado- 

 phlebia acuta, etc. 



Fig. 11.— Columnar section oi the Potomac formation. 



