80 THE PHYSIOGRAPHY OF CECIL COUNTY 



has acted on all alike, and modified all the drainage systems in a 

 similar manner. The causes which have produced this peculiar drain- 

 age are to be sought for in the past history of the region. It has 

 already been shown that the changes through which the Piedmont 

 Plateau has passed are many and complex. The region which was at 

 one period, above the ocean and undergoing erosion, was at another 

 time below and receiving sediments, only to be again raised and 

 denuded. The amount of erosion which the region underwent dur- 

 ing any one period of uplift depended on the duration of that period. 

 If the period was short, the erosion would be slight; if long, the 

 erosion would be correspondingly great. It is known that the 

 Piedmont Plateau did for a long time stand above sea-level, and that 

 during that period it suffered a vast amount of erosion. This erosion 

 interval probably began in Paleozoic time and extended to the 

 Jurassic or Lower Cretaceous. Throughout this great period, em- 

 bracing, doubtless many millions of years, the Piedmont Plateau is 

 believed to have been above sea-level; if at any time it was submerged, 

 no record of such submergence now remains. During this inter- 

 val, the Appalachian Mountains and the highlands which previously 

 existed on the site of the present Coastal Plain were gradually cut 

 down to the Schooley peneplain. Such a transformation required a 

 vast amount of time for its accomplishment; but when it was com- 

 pleted, the rivers which brought about the change had fixed their 

 courses in the softer rocks and had avoided the more obdurate ones. 

 During Cretaceous time, or probably earlier, the eastern portion of 

 the Schooley peneplain sank beneath the Atlantic, and was buried 

 under a heavy load of sediments; at a later period, the region was re- 

 elevated and appeared once more above the water iadened with these 

 deposits. On this new land surface, streams at once began to flow 

 and established their courses in harmony with the conditions there 

 presented. As the old valleys of the Schooley peneplain had been 

 filled in and obliterated, the channels now cut out and occupied 

 by the new system of rivers were entirely independent of those 

 produced by any previous streams. They were uninfluenced by 

 the buried topography and pursued their courses on the slowly 



