114 THE CAMBRIAN AND ORDOVICIAN DEPOSITS OF MARYLAND 



the siliceous formations which form its elevated east and west boundaries, 

 is in both cases a fault plane. There is little doubt as to the faulting on 

 the east side, but the evidence is not so convincing on the west side. The 

 succession there may be normal, that is, undisturbed with the Beekman- 

 town limestone lying unconformably on the Lower Cambrian Harpers 

 shale. 



The Beekmantown Limestone 



All of the numerous quarries in the Frederick Valley operated for the 

 burning of lime expose massive, rather pure, bluish limestones which 

 hold fossils of Beekmantown age. The rock itself is not unlike that of the 

 lower Beekmantown above the Stonehenge member in the Appalachian 

 Valley, so that the use of the name Beekmantown for the quarry rock 

 seems appropriate. It is even possible that the Stonehenge member is 

 represented here, for in the outcrops of Paleozoic limestone in the western 

 part of the valley, namely, along the trolley car track two and one-half 

 miles northwest of Frederick, strata with edgewise conglomerates are well 

 developed. Usually, in this part of the valley, these massive limestones 

 are covered by Mesozoic red beds. However, in two places, erosion has 

 removed the red beds so as to expose not only the quarry rock, but also 

 the underlying Harpers shale. One of these is in a small area two miles 

 south of Catoctin, the other a larger exposure just east of Braddock. 

 Fossils were not observed in either of these areas, but the lithology of the 

 limestone is precisely like that of the fossiliferous strata a short distance 

 to the east. Moreover, as shown on the map (pi. I), an area of quarry rock 

 just east of Braddock contains an infolded band of fossiliferous building 

 rock. Throughout the central and eastern parts of the valley where the 

 quarry rock frequently outcrops there can be no question regarding the 

 Beekmantown age, for here fossils are not uncommon. Along the eastern 

 edge of the valley just west of the pre-Cambrian schists there are outcrops 

 of a massive light gray laminated limestone in which the laminae are 

 much contorted and weather into a sandy shale somewhat resembling the 

 shale fragments resulting from the disintegration of the upper Stone- 

 henge member of the Beekmantown. Fossils have not been discovered in 



