150 THE CAMBRIAN AND ORDOVICIAN DEPOSITS OF MARYLAND 



Section of Chambersburg Limestone One-Half Mile South of Fort London, Pa. 



Martinsburg shale. F ee t 



Fissile shale with thin, hard, dark calcareous beds on fresh ex- 

 posure, 100 + feet, underlain by 40 feet of hard calcareous 

 dark shale and thin limestones, weathering light gray, 

 with graptolites at top. 

 Sinuites bed. 



Subgranular black crinoidal limestone containing Sinuites and 



Trinucleus 2 



Chambersburg limestone. 

 Nidulites bed. 



Dark fine-grained limestone weathering cobbly 36 



Echinospherites bed. 



Rather dark thin bedded and shaly limestone with fossils, 



among them fragments of Echinospherites . . ., 15 



Massive dark subgranular limestone 12 



Tetradium cellulosum bed. 



Pure dove-covered fine even-grained limestone, containing 



Tetradium cellulosum and Leperditia in fine conglomerate. 8 

 Pure granular and suboolitic limestone, upper beds coarsely 



granular; contains Leperditia and other ostracoda 9 



Irregularly bedded compact clayey limestone filling irregulari- 

 ties in top surface of underlying bed. Contains Helicotoma 



planulatoides, Beatricea and other fossils 1 



Caryocystites bed. 



Heavy-bedded gray granular to subcrystalline limestone; very 

 fossiliferous; trilobites, brachiopods, Caryocystites plates, 



and Solenopora 10 



Dark-blue flaggy limestone, few fossils 8 



Poorly exposed dark granular limestone, estimated 100+ 



Stones River limestone. 



Pure dove-colored limestone with Leperditia 



200+ 



An excellent section showing the three divisions usually developed in 

 this area is exposed on the banks of the west branch of Conococheague 

 Creek two and one-half miles southeast of Mercersburg, just south of the 

 Greencastle turnpike. In this section the Sinuites zone marking the base 

 of the overlying Martinsburg shale is very fossiliferous and easily recog- 

 nized. The fine-grained, pure limestone of the Stones Eiver also clearly 

 marks the base of the formation. 



