116 THE CAMBRIAN AND ORDOVICIAN DEPOSITS OF MARYLAND 



The Frederick limestone consists of thin-bedded dark blue argillaceous 

 strata separating into layers usually less than two inches in thickness. 

 On further weathering, these leave as a residual product in the soil, 

 brownish-yellow shale-like fragments quite similar to the weathered 

 Martinsburg shale of the Appalachian Valley. This limestone is often 

 much crumpled and so seamed with quartz veins that the disintegration of 

 its strata leaves numerous fragments of white crystalline quartz in the soil. 

 In freshly quarried exposures the Frederick limestone appears massive 

 and dark blue, but slight exposure to the weather causes its separation 

 into the thin flagstones so much used in this area for building fences and 

 embankments that the local name of building rock is applied to it. It is 

 less soluble than the associated purer Beekmantown limestone, so that in 

 weathering it gives rise to hill topography which is in marked contrast 

 to the lowland areas characteristic of the Beekmantown strata. The 

 dark-blue color, thin platy . layers of argillaceous composition, upland 

 topography and residual quartz fragments distinguish it readily from 

 the lighter colored, massive, purer rock referred to the Beekmantown. 



Although numerous exposures of the Frederick limestone may be seen 

 in the vicinity of Frederick, perhaps the best place to view its contact 

 with the underlying Beekmantown limestone is at the Tabler quarry 

 where a distinct line of unconformity may be noted between the two 

 formations. 



The thickness of the Frederick limestone is difficult to determine 

 because it has no recognizable upper boundary such as the succeeding 

 formation. However, in areas where it is infolded into the Beekmantown 

 limestone, its thickness seems to be not less than 200 feet. Such infolded 

 areas are well shown in the quarries at LeG-ore, Maryland. 



Although of rare occurrence fossils can be found in this limestone 

 more frequently than in the subjacent strata because the opportunities 

 for collecting are more numerous. The natural outcrops of the rock 

 seldom show organic remains, but it is only a matter of search along the 

 stone fences of the Frederick Valley to discover fossils in the thin lime- 

 stone layers of which most of them have been built. Five species have 



