MARYLAND GEOLOGICAL SURVEY 107 



of a more soluble nature and therefore weather into lowland areas again. 

 Therefore the broad area of folded Beekmantown limestones in which 

 Hagerstown is located presents a succession of elongated highland areas 

 alternating with usually broader lowland areas. This alternation in the 

 topography is well shown in Hagerstown itself, where the hills passing 

 through the town are composed of upper Stonehenge limestone and the 

 low areas between them are underlaid by lower Stonehenge or by the over- 

 lying Beekmantown limestone. 



The line of low hills formed by the upper member of the Stonehenge 

 limestone is a characteristic feature of the Beekmantown topography 

 only, as noted before, in the eastern half of the Appalachian Valley of 

 Maryland, because west of the Martinsburg shale belt the siliceous nature 

 of this -member is not so well developed and consequently weathers much 

 like the remaining portions of the Beekmantown. The marked topo- 

 graphic feature of the western belt of outcrops is a line of hills composed 

 of the chert derived from the Cryptozoon steeli zone of the formation 

 which is unusually well developed in this part of the Valley. Here speci- 

 mens of the Cryptozoon are very abundant, and as they silicify upon 

 weathering, their remains leave considerable masses of chert in the soil 

 However, the greater part of this residual material consists of yellow, 

 platy, flinty chert formed by replacement of certain layers of the lime- 

 stone. The Beekmantown limestone weathers so readily that the deter- 

 mination of the geologic structure of the formation in many cases would 

 be almost impossible were it not for this extensive development of Crypto- 

 zoon and its accompanying chert. This chert zone is plotted on the map 

 of the western part of the Valley where it gives a clue to the lower 

 boundary of the formation and also aids in determining the structure. 

 For example, the small synclinal area on the west flank of the larger 

 synclinal area three miles northeast of Clear Spring is an interesting 

 case of this zone's value in determining structural relations. 



The cauliflower chert developed at the top of the Beekmantown does 

 not occur abundantly enough or through a sufficient thickness of strata 

 to form a topographic feature, but the unusual shape of these flinty 

 objects is so characteristic that their presence in the soil is the surest 



