28 The Upper Cretaceous Deposits op Maryland 



cretaceous 

 Lower Cretaceous 



The Lower Cretaceous is represented by the Potomac Group, which 

 consists of the Patuxent, Arundel, and Patapsco formations, deposits 

 laid down under estuarine and fluviatile conditions. The three forma- 

 tions have only been recognized in their full development in Maryland, 

 the lowermost Patuxent formation not being found to the north of 

 Maryland but extending southward as the basal division of the Coastal 

 Plain series through the south Atlantic States to eastern Alabama, while 

 the uppermost Patapsco formation extends northward into Pennsylvania 

 and disappears southward in central Virginia. The Arundel formation 

 has been recognized in Maryland alone. 



The three formations are unconformable to each other and the under- 

 lying and overlying formations. They consist chiefly of sands and clays, 

 the former frequently arkosic, while gravel beds are found at certain 

 points where the shoreward accumulations are still preserved. The 

 deposits of the Patuxent formation consist mainly of sand, often arkosic, 

 and at times argillaceous, although clay beds at times appear. The 

 Arundel formation consists largely of clays, frequently dark colored, and 

 affording in places large amounts of nodular carbonate of iron. At times 

 the deposits are very carbonaceous. The Patapsco materials consist 

 largely of highly colored and variegated clays which grade over into 

 lighter colored sandy clays and also at times into sands. 



The organic remains consist largely of fossil plants, although the 

 Arundel formation has afforded representatives of several orders of 

 Eeptilia together with a few invertebrate fossils. The fossil plants in 

 the Patuxent and Arundel formations consist chiefly of ferns, cycads, 

 and conifers, while the Patapsco formation contains a considerable rep- 

 resentation of dicotyledonous types. Messrs. Berry and Lull, who have 

 studied the plant and animal remains, regard them as characteristic of 

 the Lower Cretaceous. The fossil plants of the Patuxent and Arundel 

 are strongly Neocomian-Barremian in character, while those of the 

 Patapsco are distinctly Albian. 



