76 THE CAMBRIAN AND OEDOVICIAN DEPOSITS OF MARYLAND 



an important bearing on the age determination of certain formations in 

 the Appalachian Valley. Apparently the same species occur abundantly 

 in the basal part of the Kittatinny limestone in the Lehigh Valley of 

 Pennsylvania and nearby areas in New Jersey where they are associated 

 with trilobites of the same general types as those found near Saratoga, 

 New York. 



In the Cumberland Valley of southern Pennsylvania these same species 

 of Cryptozoon are found in the basal part of a, thick series of siliceous 

 banded limestone that lies between the Middle Cambrian Elbrook lime- 

 stone and another great mass of relatively pure limestone that corresponds 

 to the well-known Beekmantown limestone of the New York section. 

 This intervening formation which is about to be described was dis- 

 tinguished and mapped by Stose in the Mercersbutrg-Chambersburg 

 (Pennsylvania) folio of the U. S. Geological Survey as the Conococheague 

 limestone, so called from the good exposures along the banks of Conoco- 

 cheague Creek near Scotland, Pennsylvania. From this place the forma- 

 tion extends in typical development to the Great Valley of Western Mary- 

 land, where its outcrops cover a considerable area. 



LITHOLOGIC CHARACTERS. The main body of the Conococheague lime- 

 stone is composed essentially of massive dark-blue, closely banded lime- 

 stones. The banding is usually one-half to one inch in width and is 

 caused by the alternation of thin, wavy, sandy laminae with thin layers 

 of purer rock. The sandy laminae are inconspicuous in the freshly 

 fractured rock, although close examination reveals the alternation of 

 the dark blue purer and gray siliceous limestone bands quite clearly. 

 Upon weathering, the siliceous laminae appear as yellowish sandy 

 streaks separating light-blue or gray bands of limestone. Further 

 weathering causes the siliceous laminae to stand out in relief as more or 

 less parallel ribs. Finally, where the rock has suffered complete disin- 

 tegration, these laminae are left in the soil as hard, siliceous thin plates. 

 Strata of this nature can be found in almost any outcrop of the formation, 

 but interbedded with them are various other types of limestone. Of these, 

 the most striking are the beds of " edgewise " conglomerate which alter- 

 nate frequently with the usual banded limestone. This conglomerate is 



