194 PHYSIOGRAPHY AND GEOLOGY OP THE COASTAL PLAIN PROVINCE. 



may be mentioned the Trinity beds of Texas, the Lakota formation of the 

 Black Hills of Dakota and Wyoming, the Kootenai formation of British 

 Columbia- and Montana, part of the Shasta group of the Pacific coast, 

 and the Kome beds of Greenland. It is also probable that the Morrison 

 beds of the Eocky Mountain district belong here. 



There has been a prolonged discussion as to the age of these beds since 

 Professor Marsh considered the Dinosauria found in the overlying Arundel 

 formation in Maryland to possess Jurassic affinities. The paleohotanists, on 

 the other hand, have consistently maintained the Lower Cretaceous age of 

 the deposits, basing their conclusions on the extensive flora which is closely 

 similar to that found in the ISTeocomian beds of Portugal, Mexico, and Japan 

 and in the Wealden deposits of England and Germany, now generally 

 regarded as of Lower Cretaceous age. More recent studies of the Dinosauria 

 have led Professor Lull to regard them also as of Lower Cretaceous age and 

 the Patuxent formation is therefore referred to that horizon in this report. 



The Patapsco Formation. 



The Patapsco formation in Virginia is similar lithologically to the for- 

 mation thus named in Maryland while the flora of the two areas is practically 

 identical. The deposits in both regions consist of highly colored and varie- 

 gated clays which grade over into highly colored arenaceous clays, while 

 coarser sandy beds are at times interstratified. 



The Patapsco formation includes the Mt. Vernon and part of the Aquia 

 series of Ward ; also part of Fontaine's Eappahannock series. 



Among the more important plant fossils found common to the two areas 



are: 



Acrostichopteris longipennis Fontaine Pinus vernonensis Ward 



Araiicarites aquiensis Fontaine Sapindopsis brevifolia Fontaine 



Araliaephyllum 7nagnifolium Fontaine Sapindopsis magnifolia Fontaine 



Araliaephylliim crassinerve (Fontaine) Sapindopsis variahilis Fontaine 



Berry Sassafras parvifoliuni Fontaine 



Celastrophyllum parvifolium (Fontaine) Widdringtonites ramosus (Fontaine) 



Berry Beny 



Celastrophyllum acutidens Fontaine Eederaephylliim dentatum (Fontaine) 

 Nelumbites tenuinervis (Fontaine) Berry Berry 



Nelumbites virginiensis (Fontaine) Ber- Podozamites lanccolatus (L. & H. ) 



ry Scliimper 



Populophyllum minutum Ward 



The Patapsco deposits are not known on the Atlantic seaboard to the 

 south of the James Eiver area but extend northward across Maryland and 

 Delaware into Pennsylvania, their most northern occurrence being isolated 

 outcrops in certain of the deeper valleys to the west of Philadelphia. 



