MARYLAND GEOLOGICAL SURVEY 59 



does not form a conspicuous element in the topography. This fifth 

 terrace is the beach and wave-built fiat which extends along the shore 

 of Chesapeake Bay and the Patuxent River. It is everywhere present 

 and its width depends in a large measure upon the force of the tidal 

 currents which sweep over it. 



When the distribution of terraces on the south bank of the Patuxent 

 Eiver is compared with that on the north bank of the Potomac, it will 

 be found that there is a much greater development of the lowest terrace 

 in the valley of the latter. This lack of harmony between the two 

 river valleys is apparently due to the erosion of the lowest terrace from 

 the south bank of the Patuxent Eiver. From Horse Landing Greek 

 southward to Cuckold Creek the lowest terrace has been almost entirely 

 removed, but just across the river on the Calvert County side this 

 terrace has an extensive development. South of Cuckold Creek the lowest 

 terrace is represented by broad flats, but is almost entirely absent from 

 the shore of Calvert County on the north bank of the river. It thus 

 appears that the Patuxent has removed this terrace first on one and then 

 on the other side of its valley. 



Taken as a whole, the divide of the county is lowest in its southern 

 portion between Chesapeake Bay and St. Mary's River, where it has an 

 elevation of about GO feet and rises gradually until its greatest altitude 

 is reached near Oaks, where it has a height of about 200 feet. 



THE DRAINAGE OF ST. MARy's COUNTY'. 



St. Mary's County, occupying, as it does, the southern extension of 

 one of the two peninsulas in Southern Maryland, is entirely surrounded 

 by water except along its northwest border, where it joins Charles Coimty. 

 Its northeastern margin is washed by the waves of the Patuxent River 

 and its eastern and southern margin by those of Chesapeake Bay, the 

 Potomac River and its estuaries. These three bodies of water receive 

 the drainage of the entire county. The divide which separates the head- 

 waters of the streams which flow into the Patuxent-Chesapeake basins 

 from those which flow into tlie Potomac River is an extremelv irregular 



