76 THE PLIOCENE AND PLEISTOCENE DEPOSITS OF MARYLAND 



STEEAM VALLEYS. 



Within the Coastal Plain of Maryland there are discernible four 

 generations of stream valleys. Three of these no longer contain the 

 streams which cut them. They have been referred to in the discussion 

 as reentrants penetrating the various terraces. The first is found de- 

 veloped as a flat-bottomed drainage way of greater or less width and 

 extent, running up into the Lafayette terrace. Its level bottom is an 

 integral part of the Sunderland terrace. The second one of these drain- 

 age ways penetrates the Sunderland terrace in a similar way. Its 

 characteristics are analogous to those entering the Lafayette terrace and 

 its flat bottom forms an integral part of the Wicomico terrace. The 

 third of these drainage ways cuts a reentrant within the body of the 

 Wicomico terrace and its level floor forms an integral part of the Talbot 

 terrace. The fourth and last of these drainage ways is now in the 

 process of formation. It is the system of valleys which are being cut 

 by the recent streams. Toward their headwaters these valleys are narrow 

 and V-shaped, and if traced to their sources, are often found to start 

 from intermittent springs surrounded by a steep-walled amphitheatre 

 from 5 to 10 feet in height (Plate IX and Plate X, Fig. 2). Toward 

 their lower courses these valleys are broad and flat and are frequently 

 filled with fresh or brackish-water marshes (Plate XX). In the upper 

 portions of their courses the valleys are being eroded. In the lower 

 portions they are being filled. A glance at the map (Plate I) will serve 

 to confirm the opinion which has been held for a long time, namely, that 

 the rivers 'of the Coastal Plain of Maryland have been drowned along 

 their lower courses, or, in other words, have been transformed into 

 estuaries by the subsidence of the region. The filling of these valleys has 

 taken place toward the heads of these estuaries (Plate XIX, Fig. 1). 

 The headwaters of these Eecent valleys are being extended inland toward 

 the divide with great rapidity. 



Many of the tributary streams occupy the reentrant valleys described 

 above. The more energetic have succeeded in carrying out all of the 

 ancient floor which formerly covered these valleys and formed a portion 

 of the various terraces. Others have left mere remnants of these valley 



