MARYLAND GEOLOGICAL SUEVEY 133 



of assisting, have shown that the Chambersburg limestone can be divided 

 into six faunal divisions or members. These members vary greatly in 

 thickness from place to place, but retain their lithologic and faunal 

 characters with little change. At no place is the composite section shown 

 in the columnar section developed, but the strata shown here represent 

 all the sedimentation so far as known, of Chambersburg age. These six 

 divisions, which with one exception have received faunal designations for 

 convenience of description, are as follows : 



Divisions of Chambersburg Limestone in Pennsylvania and Maryland 



Feet 



6. Greencastle bed. Heavy bedded impure limestones 0-200 



5. Christiania bed. Thin bedded calcareous shales and shaly limestone. 0-270 

 4. Nidulites bed. Compact dark grey thick and thin bedded limestone. .200-300 



3. Echinospherites bed. Dark blue argillaceous cobbly limestone 40-50 



2. Tetradium cellulosum bed. Fine grained dove and subgranular lime- 

 stone 0-200 



1. Caryocystites bed. Bluish coarsely crystalline to subcrystalline lime- 

 stone 0-175 



The lithologic and faunal characteristics of these divisions are described 

 in the following paragraphs : 



Caryocystites Bed. The lowest division of the general time scale rep- 

 resented in the typical exposures of Chambersburg limestone consists 01 

 dove-colored and other limestones. This division contains the Tetradium 

 cellulosum fauna and is clearly of Lowville age. West of the Martinsburg 

 shale belt in Pennsylvania, the several bands of Chambersburg limestone 

 exposed in the lowland area between the northern and southern offsets of 

 North Mountain contain a well-defined and easily recognized lentil of 

 bluish crystalline limestone reaching a maximum thickness of 175 feet. 

 This bed wedges in between the Lowville division of the Chambersburg 

 and the underlying top of the Stones River. The abundant occurrence of 

 a cystid plate of the genus Caryocystites and its apparent restriction to 

 this division makes the name Caryocystites bed appropriate. The bands 

 of outcrop containing this bed are not exposed in Maryland, but are prob- 

 ably buried under the younger strata of North Mountain and areas to 

 the west. 



