MARYLAND GEOLOGICAL SURVEY 61 



between adjoining divisions commonly is marked by one or more dis- 

 tinctive lithologic features which aid considerably in the delimitation 

 of the formations. 



THE TOMSTOWN LIMESTONE 



The lowest division of the " Shenandoah " is a thick limestone forma- 

 tion which outcrops along the eastern edge of the Appalachian Valley 

 just west of the Blue Ridge or the equivalent mountain range in a 

 narrow strip often largely covered by sandstone debris from the adjacent 

 mountain. These rocks are usually highly tilted and as a result the 

 band of outcrop is often quite narrow. In Virginia this limestone 

 received the designation, Sherwood limestone, and more recently the 

 corresponding beds in southern Pennsylvania were termed the Toms- 

 town limestone on account of their outcrop at Tomstown, Franklin 

 County. In Maryland the area of outcrop of the Tomstown limestone is 

 broader than usual because these strata are here not so sharply folded. 



TOPOGRAPHY. The Tomstown limestone is the most soluble of all the 

 formations outcropping in the eastern part of the Appalachian Valley. 

 Its outcrops therefore occur only in lowland areas. As the overlying 

 formation, the Waynesboro, is composed in large part of sandstone and 

 shale, it resists weathering and solution much more than the Tomstown 

 limestone and forms hills in contrast to the limestone valley between them 

 and South Mountain. Within this valley, however, there are long, narrow 

 elevations trending northeast-southwest which owe their origin to syn- 

 clinal infolding of remnants of Waynesboro sandstone. Some of the pro- 

 nounced hills of this valley region, however are underlain by limestone, 

 but these elevations also have resulted from differential resistance to 

 weathering, as they are formed in large part of black banded chert which 

 is a characteristic component of the upper beds of the Tomstown. A 

 good example of a Tomstown limestone valley is the lowland area in which 

 Cavetown is located with a ridge of the Waynesboro formation to the west 

 and the foothills of Harpers shale and South Mountain of Weverton sand- 

 stone on the east. 



