MARYLAND GEOLOGICAL SURVEY 73 



of the Hagerstown Valley and in a still narrower band along the extreme 

 western edge of the Great Valley. The eastern area of outcrop enters 

 the state from Pennsylvania just north of Ringgold and proceeding south- 

 ward in a strip less than a mile in width is terminated by a fault near 

 Qhewsville. South of Chewsville the throw of this fault becomes less, so 

 that the Elbrook formation reappears at the surface and continues south- 

 ward in a band averaging a mile in width paralleling the hills of the 

 Waynesboro formation on the east. At Sharpsburg beyond the extremity 

 of an infolded mass of the overlying limestone, the Elbrook is partly 

 repeated in the two limbs of the syncline and the outcrop correspondingly 

 widened. 



The western band of outcrop doubtless parallels North Mountain, hut 

 is known only from a few exposures, as almost its entire area is covered 

 by mountain wash. The beds dip steeply in these exposures, so that the 

 outcrop of the formation must be confined to a strip scarcely exceeding 

 a half mile in width. 



TOPOGRAPHIC FORM AND RESIDUAL PRODUCTS. Where the geologic 

 section is normally developed, two ranges of pronounced hills those of 

 the siliceous Waynesboro on the east, those of the siliceous limestones of 

 the Conococheague on the west flank a lowland in which the less 

 resistant limestones and shales of the Elbrook are at the surface. However, 

 this lowland band is not a simple valley, but is divided longitudinally 

 into two narrow valleys by a series of low hills due to the relatively 

 resistant beds of siliceous limestone and dolomite that occur in the middle 

 part of the Elbrook. 



The topographic form of the Elbrook is not unlike that of the Toms- 

 town and the shale fragments left in the soil from both formations arc 

 quite similar. In areas where the intervening Waynesboro formation is 

 cut out by faulting, such as the area about five miles southeast of Hagers- 

 town, great care must be exercised in discriminating the two formations. 

 Determined search in areas of Tomstown limestone will sooner or later 

 reveal outcrops of the characteristic sheared marble which on weathering 

 leave the shale-like residual fragments. On the other hand, in an Elbrook 



