94 THE GEOLOGY OF CALVERT COUNTY 



lie unconformably on whatever rocks are beneath them. The clay, peat, 

 loain, sand, gravel, and ice-borne boulders, out of which they are com- 

 posed, occur in irregular beds or are developed in lenses. They arc 

 mixed together in varying amounts and grade over into each other both 

 horizontally and vertically. Two of the formations, the Sunderland and 

 Talbot, carry determinable vegetable remains, and the latter has yielded 

 in addition fragments of fossil insects. The various members of the 

 Columbia are developed in terraces lying one above the other in order 

 of their age, the oldest occupying topographically the highest position 

 (Fig. 1). They all dip gently toward the surrounding waters and to- 

 gether are widely distributed over the surface of the county and obscure 

 in a great measure the older deposits which lie beneath them. 



THE SUNDERLAND FORMATION. 



The Sunderland formation has been named from its typical develop- 

 ment near the hamlet of Sunderland in Calvert County. It consists of 

 a wave-built terrace, which was formed by the waters of the Atlantic 

 Ocean or its estuaries when the country stood at a lower level than to-day. 

 It is distributed over the entire county occupying the divides between 

 the headwaters of the principal streams. Since the time of deposition, 

 the Sunderland formation has suffered extensively from erosion. Water- 

 ways have opened up their valleys through it and have transformed a 

 once continuous mantle of loam and gravel into a series of isolated 

 patches with sinuous outlines occupying the higher portions of the 

 county, and its once level surface has now been changed by the same 

 processes into a gently rolling upland. 



Areal Distribution. 

 The Sunderland formation is the most widely developed of the Pleis- 

 tocene deposits in Calvert County. It occupies the highest divides from 

 the northern margin of the region at Lyons Creek southward to the 

 vicinity of Drum Point. Along the western border of the county in the 

 valley of the Patuxent Eiver, as well as in many of the streams which 

 penetrate it, the Sunderland is surrounded by the younger formations 



