MARYLAND GEOLOGICAL SURVEY 117 



of clay present in this formation which doubtless have some value. They 

 consist of lenses of bluish-green to black plastic clay which have been 

 exposed through wave-cutting along the Bay and the Potomac Eiver in 

 the southern portion of the county. The best exposures of this material 

 occur along the Bay shore about 5 miles south of Cedar Point, at Wailes 

 BlufiE, along the Potomac Piver, about 1 mile north of Cornfield Point, 

 and on the east shore of Breton Bay, about one-fourth mile below 

 Lovers Point. Similar clays occurring at Bodkin Point near the mouth 

 of the Patapsco Eiver have been tested and described by Dr. Heinrich 

 Eies.' He states that the clay " burned to a good red color under 

 ordinary conditions and to a deep brown when vitrified. Before this 

 clay could be used in large ware it would be necessary to add sand to 

 prevent excessive shrinkage." In certain outcrops these clays contain 

 sufficient vegetable material to render them unfit for use but in others 

 they contain very little organic matter. 



THE SANDS. 



Since the arenaceous phase predominates in almost every formation 

 represented in the region, the county contains an unlimited supply of 

 sand. The sand of the Pleistocene is used locally for building purposes, 

 but since it is so readily obtained in all parts of the county no pits of 

 any considerable size have been opened. It is said to be a fairly good 

 building sand yet no better than quantities of sands in other parts of the 

 State, hence the demand for it is purely local. 



In some places the quartz sands of the Miocene seem to be pure enough 

 for glass-making, suggesting the Miocene glass sands so extensively ex- 

 ploited in southern New Jersey, although they have never been used for 

 that purpose in this region. Careful chemical analyses and physical 

 tests, which have not been made, would be required to determine their 

 usefulness in this respect. 



Locally, the Pleistocene sands are rich in ferruginous matter which, 

 in places, cements the grains together forming a ferruginous sandstone. 



'Md. Geol. Survey, vol. iv, 1902. 



