176 THE COASTAL PLAIN FORMATIONS OF CECIL COUNTY 



portion of the Potomac group lying beneath the Patapsco formation. 

 On the strength of this evidence the Patnxent formation has been 

 tentatively referred to the Jurassic period. 



The Patapsco cycle of sedimentation came to a close with the up- 

 lifting of Cecil county once more above the surface of the water. 

 This uplift was of sufficient duration to permit another extensive de- 

 nudation of the surface before the region sank again beneath the 

 waves. This submergence ushered in the Paritan cycle of sedimen- 

 tation, during which the Paritan formation was deposited. This 

 formation, like the two preceding, was also an estuarian deposit laid 

 down in shallow water in the midst of currents constantly changing 

 in direction and intensity. Its plant remains embraced, like the 

 preceding formation, both endogens and exogens, the exogens exhibit- 

 ing strongly marked modern affinities. The re-elevation of the region 

 closed the Paritan cycle of deposition and brought that formation in 

 turn, above the level of the ocean, and subjected it to the destructive 

 work of sub-aerial erosion. 



Before leaving the record of the formations belonging to the Po- 

 tomac g*roup, a word should be said regarding the nature of the body 

 of water in which they were deposited. After a careful study of the 

 formations, not only in Cecil county, but in neighboring regions to 

 the north and south, it has been determined that the sediments are not 

 such as can be ascribed to deposits formed in the open ocean. They 

 partake rather of the character of sediments laid down in bodies of 

 brackish water where the direct influence of the sea has been elimi- 

 nated. It is believed, therefore, that the formations of the Potomac 

 group were deposited in a sound or an estuary of brackish water, 

 which was separated from the main ocean by a land barrier. The 

 position of this land mass has given rise to some discussion, and from 

 the nature of the case, can never be definitely determined; but it 

 probably was located somewhat east of the present Atlantic coast-line. 



SEDIMENTARY RECORD OF THE UPPER CRETACEOUS FORMATIONS. 



The erosion interval which followed the uplift of the Paritan for- 

 mation was brought to a close by the sinking of Cecil county once 



