110 THE CAMBRIAN AND ORDOVICIAN DEPOSITS OF MARYLAND 



extending from a line passing through Security, three miles east of 

 Hagerstown, to a northeast-southwest line west of Williamsport where a 

 fault brings the limestone in contact with the Martinsburg shale. The 

 broad expanse of Conococheague limestone in southern Maryland reduces 

 the width of the Beekmantown here from a belt almost seven miles wide 

 at the Pennsylvania state line to less than three at the Potomac. South 

 of Hagerstown the Conococheague and Beekmantown limestones are 

 intimately folded together, exhibiting characteristic Appalachian pitch- 

 ing anticlines and synclines. The western edge of this belt is a fault line 

 except at the extreme northern and southern ends where the normal 

 sequence is resumed. This fault is clearly shown at Williamsport where 

 the middle limestone of the Beekmantown may be seen in contact with 

 the lower Martinsburg shale. North of Williamsport the displacement 

 of this fault is greater and brings the Beekmantown in contact with the 

 upper sandy portion of the Martinsburg. Infolded in this large area 01 

 Beekmantown are elongated, narrow bands of the purer limestones of the 

 succeeding Stones Eiver formation. 



In the area west of the Martinsburg shale plateau the Beekmantown 

 limestone likewise occupies about one-half of this part of the Appalachian 

 Valley, but here closely folding with the Conococheague limestone causes 

 each formation to appear at the surface in elongated, more or less parallel 

 bands. The continuity of these bands is broken in the northern part of 

 the state by a transverse fault. West of the eastern base of North 

 Mountain no rocks of Beekmantown age are exposed. 



The surface rock of a considerable portion of the Frederick Valley 

 belongs to the red beds of Triassic age, but of the limestone portion of 

 the valley about one-half is occupied by strata referred to the Beekman- 

 town. These Beekmantown areas occupy in general the eastern half of 

 this portion, although folding brings small areas to the surface in the 

 western half. Two small areas just east of Catoctin Mountain are of 

 interest because erosion of the red beds has proceeded far enough to 

 expose the underlying Beekmantown strata. 



