80 THE CAMBRIAN AND OKDOVICIAN DEPOSITS OF MARYLAND 



product of these basal beds is a scoriaceous chert which occurs in great 

 quantity in the soils derived from their weathering. These chert masses 

 are sometimes several feet in diameter, and while they are composed of 

 crystalline milky quartz, they are so iron stained and cavernous that they 

 have the appearance of slag or volcanic material. Fences composed of 

 this chert are not uncommon in both the northern and southern areas of 

 outcrops and they are good evidence that the dividing line between the 

 Elbrook and Conococheague formations is close at hand. Good examples 

 of such fences may be seen on the Antietam battle-field just north of 

 Sharpsburg along the Hagerstown turnpike. 



The main mass of the formation is described in preceding paragraphs. 

 The upper beds of pink marble are very much like similar strata in the 

 overlying Beekmantown limestone. However, there is no occasion to 

 confuse the two since the usual siliceous banded rocks of the Conoco- 

 cheague are intercalated with these purer strata. Besides, the soils 

 derived from these upper beds contain abundant fragments of black to 

 yellow chert and milky vein quartz. Such siliceous residuals are char- 

 acteristic of the Conococheague, but not of any part of the Beekmantown. 



The above remarks apply particularly to the formation as developed 

 east of the Massanutten syncline. West of the great shale belt in Mary- 

 land the general features of this limestone remain about the same, with 

 the exception that 600 or more feet of massive sandy dolomite are inter- 

 calated between the usual sandy laminated limestones and the overlying 

 Beekmantown limestone. These sandy dolomites weather into sandstones 

 which strew the ground with large and small blocks. These sandstones 

 are coherent enough at times to have been used in the past as a local 

 source of grindstones. More extended study in neighboring states will 

 probably show that these upper sandy dolomites represent the eastward 

 extension of strata which do not really belong with the typical Conoco- 

 cheague limestone. However, until such studies have been made it is 

 thought advisable to classify these upper sandy beds provisionally with 

 the Conococheague limestone. A good section of this upper member may 

 be seen in the Western Maryland Railway cut just west of Charlton, 



