174 THE COASTAL PLAIN" FORMATIONS OF CECIL COUNTY 



tion of the sediments now represented by the mica-gneiss and the de- 

 position of the Triassic sediments the land was below the waters 

 of the ocean, the evidences of such submergence have all been re- 

 moved from the area of Cecil county. 



SEDIMENTARY RECORD OF THE POTOMAC GROUP. 



"With the opening of Potomac time, a new chapter in the develop- 

 ment of Cecil county began. The deposits which have recorded its 

 geological history from that time down to the present, are all uncon- 

 solidated, and collectively constitute the Coastal Plain formations. 

 They show, as a whole, a remarkable unsteadiness of the continental 

 border, for Cecil county has been either in part or as a whole, lifted 

 above the ocean level and depressed beneath the sea, not less than ten 

 times, and possibly many more. These oscillations of the coast-line 

 were not confined to Cecil county but affected also neighboring re- 

 gions of great extent. The disturbances have been recorded as un- 

 conformities between the various formations. The unconformities, 

 however, are with few exceptions not striking to the eye, but are only 

 to be observed when the region is studied as a whole, and the indi- 

 vidual beds traced foot by foot over the entire district where they 

 are developed. 



The sedimentary record of the Potomac group opens with the depo- 

 sition of the Patuxent formation. This deposit consists of clay, sand, 

 gravel and arkose. In the laminae of clay and sand are numerous 

 remains of plants which flourished on land while the sediments were 

 being deposited off-shore in the water. Tbe materials which go to 

 make up the body of the Patuxent formation are frequently cross- 

 bedded, and change rapidly in their composition, not only vertically 

 but also horizontally. The whole constitution of the formation indi- 

 cates that it was deposited in shallow water not far from shore, and 

 where currents were constantly changing in intensity. At the close 

 of Patuxent time Cecil county was elevated above the waters which 

 had deposited the Patuxent formation. The extent of this elevation 

 will never be known, for the unconformity is now only in part visible. 

 How far it runs out under the Eastern Shore is of course a question 



