MARYLAND GEOLOGICAL SURVEY 147. 



Section of Upper Divisions of Chambersburg Limestone at Greencastle, 



Pennsylvania 



Martinsburg shale. Feet 



Black fissile shale at top and shaly limestone below, not well 



exposed ... 



Chambersburg limestone. 

 Greencastle member. 



Rather massive, dark blue fine grained limestone with gastro- 

 pods and hemispheric bryozoa 40 . 



Argillaceous cobbly limestone, sandy at base 8 



Massive grey to dark blue fine grained fossiliferous limestone. 



Nidulites abundant at base 50 



Massive gray to blue subcrystalline limestone 12 



Sandy shales 8 



Massive granular limestone 60 



Sandy limestone and sandstone 20 



Christiania bed. 



Argillaceous thin bedded limestone with Christiania trento- 



nensis, etc. (exposed at southwest end of bridge) 



Nidulites bed. 



Massive grayish limestone with Nidulites fauna. (Underlying 



strata not exposed) 



This eastern band of outcrop continues into Maryland, but disappears 

 by faulting about a mile south of Cearfoss. The exposures of the' Cham- 

 bersburg in this part of Maryland are extremely poor, but the formation 

 can be clearly recognized by the cobbly appearance of the weathered rock. 

 No section could be made in this part of the state, nor were the rocks well 

 enough exposed in the southern part in the big bend of the Potomac 

 River where the formation outcrops again. 



Sections West of Martinsburg Shale Belt in Pennsylvania. In south- 

 ernmost Pennsylvania numerous belts of Chambersburg limestone are 

 brought to the surface by the geologic structure which causes the great 

 cove in North Mountain in which Mercersburg is situated. This low- 

 land area affords numerous sections of the limestone and many 

 excellently preserved fossils have been collected. These sections are .par- 

 ticularly interesting because they contain beneath the Tetradium cellulo- , 

 sum bed, which forms the base of the Chambersburg in the eastern lines , 

 of outcrop, a subcrystalline, massive limestone reaching 100 + feet in.- 

 thickness, characterized by a fauna which is related to both Chazyai^ arid. 

 Black River faunas. Another interesting feature is that the Christiania 



