MARYLAND GEOLOGICAL SURVEY 177 



more beneatli the water. This submergence differed from those 

 which had occurred in Potomac time in that the county was lowered, 

 not beneath a lagoon, but beneath the open Atlantic Ocean. The 

 deposits which compose the Upper Cretaceous formations consist of 

 clay, sand and greensand. These materials, although they are found 

 to change gradually from one area to another, yet maintain re- 

 markable uniformity, both vertically and horizontally, over great 

 areas. In New Jersey the predominant feature of this group is the 

 presence of vast beds of greensand. In Cecil county, however, and 

 the same is true southward, greensand has largely given place to ordi- 

 nary quartz sand, both fine and coarse. This change in the char- 

 acter of the materials would seem to indicate that the deposits in Cecil 

 county were deposited nearer the old shore-line, and in shallower 

 water than those further to the north. Fossil remains, such as they 

 are, consist of marine animals. They are not numerous and are un- 

 fortunately in a poor state of preservation. The evidence, as a whole, 

 points to the fact that the formations of the Upper Cretaceous were 

 deposited in the open ocean at moderate depths. 



The two formations, Matawan and Monmouth, which represent the 

 Upper Cretaceous in Cecil county, are not separated by an unconform- 

 ity as are the formations of the Potomac group but pass into each 

 other with imperceptible gradations. From this it appears that the 

 oscillations which disturbed the region during Potomac time ceased 

 during Upper Cretaceous time; or if they were present, were not of 

 sufficient amplitude to be recorded by those portions of the Upper 

 Cretaceous deposits now remaining. This cycle of deposition was 

 brought to a close by an elevation of the country above the level of 

 the Atlantic Ocean. A long period of erosion followed this uplift, 

 which was finally brought to a close by the submergence of the re- 

 gion once more. 



SEDIMENTARY RECORD OF THE AQUIA FORMATION. 



The submergence which brought Cecil county once more beneath 

 the Atlantic Ocean ushered in the cycle during which the Aquia 

 formation of Eocene age was deposited. This, in many of its char- 



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