178 THE COASTAL PLAIN FORMATIONS OF CECIL COUNTY 



acteristics, resembles closely the preceding deposits. The materials 

 are mainly sand and greensand, and the fossils which have been dis- 

 covered, are marine. The evidence then would seem to indicate 

 that the conditions which existed during the cycle when the Upper 

 Cretaceous formations were deposited, were repeated, when the 

 Aquia formation was made, for it seems to have been laid down off- 

 shore on the bed of the open ocean in water of moderate depths. An 

 elevation of the region brought this formation in its turn above the 

 ocean, and closed the cycle of its deposition. 



SEDIMENTARY RECORD OF THE LAFAYETTE FORMATION. 



The next younger formation which is present in Cecil county, is 

 the Lafayette, although in some of the neighboring counties a number 

 of formations belonging to the Miocene period are interpolated be- 

 tween the Aquia and the Lafayette. No record of these Miocene 

 beds have been discovered in Cecil county, and if they ever existed 

 there, they have been entirely removed. The depression, which 

 opened the Lafayette period of deposition carried the whole of Cecil 

 county beneath the sea; probably not even the highest points in its 

 topography remained above the surface of the water. The cycle of 

 deposition which followed was of sufficient duration to bury the an- 

 cient surface of Cecil county under a heavy load of clay, sand and 

 gravel. The source of these materials was in the Piedmont Plateau 

 and the Appalachian Mountains. The former appears to have been 

 undergoing sub-aerial decay for a long time, so that its surface was 

 covered with a mantle derived from its disintegrated crystalline rocks. 

 In such a mantle, the more easily decayed rocks would be reduced to 

 clay and sand, while the more obdurate veins of quartz would yield 

 a large number of loose stones lying in confusion on the surface. 



With the advance of the Lafayette sea, the quartz fragments were 

 concentrated by the waves on the beach, while the finer particles were 

 swept out by the undertow and deposited in deeper water. To the 

 whole was added such material as could endure the journey from the 

 more distant mountain regions. After Cecil county had received a 



