C 



I) 



112 THE CAMBRIAN AND ORDOVICIAN DEPOSITS OF MARYLAND 



This large amount of silica renders the rock unfit for the manufacture 

 of lime, which at present is the chief use to which the Frederick Valley 

 limestones are put. From the thin-bedded belt the limestone passes into 

 a more earthy facies and grades into dark colored calcareous shales and 

 these again into slates or into sandy shales." 



7T, 



FlG. 12. STRUCTURE SECTIONS ACROSS FREDERICK VALLEY. 



A. Devilbiss Bridge east through McAleer. 



B. Braddock Heights east through Frederick. 



C. East-west section through Frederick Junction. 



D. East-west section through Buckeystown. 



Tn Newark sandstone and shale. 

 Tnc Newark conglomerate. 

 Ob Beekmantown limestone. 



SYMBOLS. 



Of Frederick limestone. 



Ch Harpers shale. 



Cw Weverton sandstone. 



Ol Loudon formation, 

 Ac Catoctin schist. 



Keyes found a few species of fossils in these limestones which led him 

 to suggest that the whole series was equivalent to the Chazy, Trenton, 

 and Hudson River formations. The determination of the age and 

 structure relations of the Frederick Valley limestones was a matter of 



