MAEYT.AND GEOLOGICAL. SURVEY 129 



ing currents, as do also the abrupt changes in the character of the 

 materials, both horizontally and vertically. The presence of numer- 

 ous land plants in the clays shows the proximity of the land. 



The deposition of the Patuxent formation was ended by an uplift 

 or warping in which many of the stream valleys were occupied 

 for a portion of their courses by bogs and swamps of the Arundel 

 formation. In these marshes there was an extensive development of 

 plant life and in them also were deposited iron ores that are now of 

 considerable value. After an uplift and interval of erosion the 

 land was again depressed beneath sea level. Physical conditions 

 similar to those which had prevailed during Patuxent time existed 

 during this period of submergence, in whicli the Patapsco formation 

 was laid down. Dicotyledonous plants, Avhich are very rare and 

 primitive in structure in the Patuxent deposits, are abundant in the 

 Patapsco and belong to higher types. This seems to indicate that a 

 long time intervened between the two periods of deposition, during 

 which the land flora of the region materialh' changed. After the 

 deposition of the Patapsco formation the region again became land 

 through an upward movement which drained all the previously exist- 

 ing estuaries and marshes. Erosion at once became active and the 

 Patapsco surface was dissected. 



SEDIMENTARY RECORD OF THE UPPER CRETACEOUS. 



A downward land movement again submerged the greater portion 

 of the region, leaving only a very narrow strip of Patapsco deposits 

 above water. The Raritan formation Avas next deposited, under con- 

 ditions very similar to those which had existed during the previous 

 submergence. Raritan deposition was terminated by an uplift which 

 again converted the entire region into land. 



The widespread development of shallow-water deposits, everywhere 

 cross-bedded and extremely variable in lithologic character, and the 

 presence throughout these deposits of land plants furnish some evi- 

 dence that sedimentation took place not in open ocean waters 

 but in brackish or fresh-water estuaries and marshes that were 

 indirectly connected with the ocean, which may have at times locally 



