88 The Upper Cretaceous Deposits of Maryland 



differentiation from the beginning to the end of the Matawan time, and 

 although some variations in sedimentation took place, there is no ade- 

 quate basis for anything but local divisions of the strata. 



It is probable that this depression so characteristic of Matawan time 

 may have carried the sea over the area of earlier Cretaceous sediments 

 and on to the Piedmont district, for we find widely scattered through the 

 beds, particularly in the lower strata, a very pronounced admixture of 

 mica flakes making the micaceous sandy clays of this formation among 

 the most diagnostic deposits. No adequate source for these materials can 

 be found in the earlier Coastal Plain formations and it seems likely that 

 they must have been derived from the Piedmont gneisses, either through 

 direct coastal contact or by transportation down the wide rivers into 

 the sea. 



The Matawan sediments now preserved in Maryland and farther north 

 show that clearly defined marine conditions had been established over the 

 entire district, but farther soitth in North Carolina the repetition of 

 marine and nonmarine sediments went on during Magothy and Matawan 

 time as shown in the Black Creek beds of that area. It is evident, there- 

 fore, that no great interval of time could have elapsed after the close of 

 the Magothy and the opening of the Matawan, although pronounced 

 physical changes are apparent in the Maryland area. 



A much greater change, however, marked the close of the Matawan, and 

 although marine conditions still persisted a very considerable change had 

 taken place in the faunas, while the oscillations of the sea floor caused the 

 transgression of the Monmouth strata southward over the Magothy 

 deposits with the complete overlapping of the Matawan formation. This 

 marked change in the fauna and to some extent also in the sediments 

 indicates that physical and faunal changes of no mean proportions had 

 been initiated. This faunal change has now been traced all the way from 

 New Jersey to the Gulf, and is one of the significant divisional lines in 

 the Cretaceous deposits of the Atlantic border. 



The greatly increased proportion of glauconite in the sediments sug- 

 gests somewhat deeper, or at least more open, seas, free from the influence 



