1892] MARYLAND ACADEMY OF SCIENCES. 193 



The Alternate Clay Sands have been carried away from 

 the slopes and summits of the ridges of Variegated Clays 

 on the Patuxent river east of Bovv^ie, so that the white 

 sandstone now rests at all angles and at several levels, 

 from near the present bed of the stream to about thirty 

 feet above, in the sides of the hills. 



The name Albirupean was applied by the writer in Jan- 

 uary, 1888, to a wide-spread series of sand, sandstone and 

 clay strata unconformably overlying the Potomac forma- 

 tion of Mr. McGee, but a part of which that writer in- 

 cluded in his description of the formation.* Later, Prof. 

 Fontainef described a large number of fossil plants, chiefly 

 from Virginia, which he referred to this Potomac forma- 

 tion, and at the same time gave a summary of his views 

 relative to the structure, composition and extent of the 

 formation. 



My own studies of the deposits at Fredericksburg, Va., 

 and other places between that city and Mount Vernon, in- 

 duce me to take a very difterent view from Prof. Fontaine 

 of the structure of the region, and of the position held by 

 the fossil plants in the order of tlieir succession in time. 



The following facts have influenced my belief in the 

 theory of succession of the strata or beds and their con- 

 tents : The lowest iron ore clays, at the base of which the 

 most archaic types of Angiosperms occur, are those beneath 

 Federal Hill and its connections in Baltimore. The same 

 series of clays is identifiable in many places all the way 

 from near the North East river, at the head of Chesa- 

 peake bay, to the District of Columbia. Local areas of 

 similar clays which have not yet yielded their character- 

 istic plant fossils occur in Virginia, west of the Potomac 

 river. Near Falmouth and at a few points between that 

 place and Fredericksburg, Va., are clays of the same plastic 

 type and structure as those in Federal Hill. 



* McGee : Geology of the Head of Chesapeake Hay ; 1888, p. 615. 



t Fontaine : Potomac, or Younger Mesozoic Formation ; 1889, p. 47. 



