Introduction 



support a flora of great variety and richness, including many- 

 species rare or non-existent on the Coastal Plain. 



The surface of this upland region is largely composed of rocks 

 which are among the most ancient in the United States. They 

 belong to the Pre-Cambrian age, and contain no fossils. Among 

 them are extensive areas of schists, diorites and gabbro, the last 

 locally known as ''Brand wine granite." They yield predominantly 

 acid soils. Serpentine rock, with its characteristic flora, appears in 

 Delaware as a single outcrop, about M by 13^ miles in extent, 

 situated east and northeast of Mount Cuba. There are several 

 much more extensive outcrops of serpentine along the northern and 

 northwestern borders of Cecil County, Maryland. Limestone 

 appears to reach the surface in but one locahty in Delaware, namely 

 at the Eastburn quarries along Pike Creek, east of Pleasant Hill. 

 However, this region seems to be lacking in Hme-loving plants. 



The Coastal Plain. South of the Fall Line the present surface 

 of the land, in general, has an altitude only sHghtly above sea-level. 

 If the level of the ocean should rise as much as fifty feet, most of 

 the Peninsula south of Cecil and New Castle Counties would be 

 reduced to an archipelago of small low islands, and the two Virginia 

 counties would be entirely submerged. A rise of 100 feet would 

 obhterate all but the northern extremity of the peninsular Coastal 

 Plain. 



The oldest formations which appear on the Coastal Plain of the 

 Peninsula belong to the Lower Cretaceous, and occur chiefly on 

 Elk Neck, in the region lying north and west of Charlestown, and 

 in the drainage areas of the Elk River and Christiana Creek. 



The soil of our portion of the Coastal Plain consists for the most 

 part of sands, loams and gravels, of marine deposition during early 

 Pleistocene times. These soils are underlain by much older forma- 

 tions, which are exposed along stream valleys in the northern half 

 of the Peninsula. In the material dredged from the bed of the 

 Chesapeake and Delaware Canal, fossil remains of belemnites and 

 giant clams belonging to Upper Cretaceous times, occur in abun- 

 dance, especially along the recently excavated Reedy Point channel. 

 Elsewhere, fossil wood (lignite) abounds in the excavated material. 

 "Greensand marls," also of Cretaceous age, are exposed in many 

 stream valleys, and are conspicuously in evidence on the slope of the 

 deep cut of the canal, just east of Summit Bridge. 



The recent geological history of the Peninsula is one of gradual 



XI 



