82 THE CAMBRIAN AND ORDOVICIAN DEPOSITS OF MARYLAND 



Stonehenge member of the overlying Beekmantown limestone. This area 

 of outcrop therefore has a general monoclinal structure since younger 

 beds border it on the west and older beds pass beneath it on the east. East 

 of Hagerstown, Security on the west and Chewsville on the east mark 

 the boundaries of the outcrop which averages three miles in width. 

 Numerous exposures of the typical limestone may be seen along the 

 Western Maryland Eailway between Chewsville and Security and at the 

 latter place the large quarry of the Security Cement and Lime Company 

 exhibits a considerable section of the upper beds (see pi. XII, fig. I). 

 Leitersburg, five miles northeast, stands on a rocky ridge of Conoco- 

 cheague limestone, the rock here belonging to the lowest beds as evidenced 

 by the scoriaceous chert found in abundance in the vicinity. South of 

 Hagerstown the width of the belt of outcrop increases to over five miles, 

 and a wide, unbroken expanse of this limestone occurs along the Potomac 

 and for some miles northward. In many places here the beds are either 

 very gently folded or almost horizontal. 



In the western half of the Valley the outcrops of the Conococheague 

 consist of several narrow belts of strata brought to the surface in the 

 lowland area between the shale highland on the east and the front range 

 of the Alleghenies on the west. Here the areas of outcrop are marked by 

 many chert fragments and sandstone debris left in the soil. 



AGE AND COERELATION. Only a small number of species of fossils has 

 so far been discovered in the Conococheague limestone, these consisting 

 of calcareous algae occurring in the basal beds ; several brachiopods and 

 trilobites found in the upper strata, and a large species of alga near the 

 top of the formation.- The two calcareous algae (Cryptozoon proliferum 

 Hall and C. undulatum new species) at the base of the formation are 

 found in abundance wherever these beds are exposed. The large Crypto- 

 zoon near the top is a not uncommon fossil, but the trilobite, Saukia 

 stosei Walcott, and the brachiopod, Eoorthis cf. desmopleura (Meek), are 

 of very rare occurrence in the higher beds. The trilobite has been found 

 only in the Cumberland Valley, so it is of little value for exact correlation. 

 Still it belongs to a genus that is elsewhere represented only in late Upper 



