68 PHYSIOGRAPHY AND GEOLOGY' OF THE COASTAL PLAIX PROVIXCE. 



and occasionally lithified. The Virginia deposits are in general much less 

 highly colored than those of the Maryland region, a feature due to the 

 absence of iron rich crystallines in the area from which their sediments 

 were derived. The clays, like those of the Patuxent in Virginia are 

 frequently greenish when unweathered, due to the presence of chlorite de- 

 rived from the chloritic schists of the Piedmont. 



Strike, dip and tJiickness — The strike of the Patapsco beds in Virginia is 

 almost due north and south and the dip is about 30 feet to the mile to the 

 eastward. The total thickness in the region of outcrop is about 150 feet, 

 but this increases to the eastward beneath the overlying Tertiary deposits. 



Paleontologic character. — The Patapsco deposits have yielded a few 

 specimens of undeterminable unios and an extensive flora made up of 

 ferns, cycads, conifers, monocotyledons and dicotyledons. The ferns, 

 cycads, and conifers represent the dwindling remnants of the Patuxent and 

 Arundel flora, quite a number of the older Potomac species continuing 

 through the Patapsco as for example Nagciopsis angustifolia Font., and 

 various species of Cladophlehis, Onychiopsis, Sequoia, and Spheiiolepis. 

 In other cases the same genera are represented by distinct species at the 

 two horizons as in the genus Acrostichopteris. 



A species of Pinus represented by seeds, cone-scales, and cones is one 

 of the characteristic forms of this formation as are also the cone-scales 

 referred to Araucaria aquiensis Font. The twigs of Widdringtonites ramo- 

 siis (Font.) Berry are also a rather constant feature of the Patapsco 

 fossiliferous outcrops and furnish a point of contact with Widdringtonites 

 Reichii (Ett) Heer of the Upper Cretaceous. Other characteristic Patapsco 

 forms are the various species of the dicotyledonous genus Sapindopsis and 

 the fern Knowltonella Maxoni Berry. The marked distinctness of the 

 Patapsco flora, however, rests mainly upon the great increase and modern- 

 ization of the dicotyledons which foreshadow those of the Raritan. 



The more characteristic of these are various species of Sapindopsis, 

 Celastrophyllu'ni. Sassafras, Sterculia, Cissites, Aralcephyllum, Fopulo- 

 phylhnn, etc. 



Arcal distribution. — -The Patapsco formation has been recognized in 

 isolated remnants in Pennsylvania and Delaware, it outcrops in a broad 

 belt across Maryland, and continues southward into Virginia through 

 eastern Fairfax, Prince William, and Stafford counties to the vicinity of 

 Fredericksburg. It is most extensively developed in the valley of the 

 Potomac Eiver, appearing in numberless bluffs from Washington to where 

 it finally disappears beneath the Eocene in the vicinity of Aquia Creek, 



