7o8 GEORGE W. STOSE 



this formation. In general the formation is composed of three 

 divisions : — a middle band of massive pure granular limestone contain- 

 ing the large gasteropod Madurea magna and thin beds of black chert 

 that weather into small rectangular blocks ; an upper series of thin- 

 bedded pure limestone ; a lower series of interbedded massive pure 

 beds and magnesian layers. 



These divisions cannot be readily distinguished in all parts of the 

 area, and at no place can the complete section be seen because the 

 beds are several times repeated by folding and the outcrops are not 

 continuously exposed. 



The following is a composite section of the formation in the Cham- 

 bersburg belt: 



Feet 



Thin-bedded, fine-grained, pure, dove limestone. 275-!- 



Massive pure limestone containing Maclurea magna and^black chert layers. 

 Upper part, compact, blue to dark; lower part, light gray, granular 



and oolitic 150-200 



Massive and thin-bedded limestone interbedded with magnesian layers . 600+ 



Total 1050 -f 



In the western belts the cherty Maclurea horizon was not clearly 

 observed and the three-fold division could not be made. At West 

 Branch of Conococheague Creek, south of the Mercersburg- Green- 

 castle pike, its thickness was determined at 800 to 1,000 feet. 



In McConnellsburg Cove, west of Tuscarora Mountain, the 

 exposures are exceptionally meager. At a quarry south of the 

 Mercersburg pike the formation as exposed comprises about 575 

 feet of interbedded, pure and banded magnesian beds with very pure 

 fine-grained dove limestone at the top. 



The formation crosses the Mercersburg and Chambersburg quad- 

 rangles from north to south in five belts. The eastern belt lying in the 

 Chambersburg quadrangle is intricately folded and faulted, and com- 

 prises several parallel strips. 



In the next limestone belt to the west, the Welsh Run-Edenville 

 anticline, the Stones River forms a narrow strip about J mile in 

 width on either side of the Beekmantown. In the Mercersburg belt 

 it occurs as two narrow faulted strips. In the Foltz and McCon- 

 nellsburg limestone belts, its outcrops are largely covered. 



