154 THE CAMBRIAN AND ORDOVICIAN DEPOSITS OF MARYLAND 



however, the Chambersburg limestone is most important since its con- 

 tained faunas are more numerous in species and individuals than any 

 other formation. 



Just north of the Maryland-Pennsylvania state line the areas of out- 

 crop of the Chambersburg limestone are not only more numerous, but 

 also often broader. Here also natural and artificial cuttings have af- 

 forded much better opportunities to study the formation and to collect 

 its faunas. The identification of the Chambersburg fossils described in 

 the following pages has been based primarily upon the much better pre- 

 served material from Pennsylvania, although the Echinospherites and 

 Mdulites beds in Maryland have yielded equally good faunas. The 

 divisions of the Chambersburg limestone and their approximate position 

 in the time scale are as follows : 



Divisions of Chambersburg Limestone in Pennsylvania and Maryland 



Greencastle bed (Late Black River or Early Trenton) 



Christiania bed (Late Black River) 



Nidulites bed (Late Black River) 



Echinospherites bed (Late Black River) 



Tetradium cellulosum bed (Early Black River-Lowville) 



Caryocystites bed (Upper Chazyan or Earliest Black River) 



The relations of these faunas to each other and the distribution of their 

 strata in different portions of the middle Appalachian valley have been 

 described on previous pages. 



UPPER ORDOVICIAN SHALES 

 THE MARTINSBURG SHALE 



The shale phase of sedimentation which concludes Ordovician deposi- 

 tion in the Middle Appalachians is best known from outcrops in the 

 middle of the Great Valley where these strata occupy part of the well- 

 known syncline named from Massanutten Mountain in Virginia. Mar- 

 tinsburg, West Virginia, lies on the western edge of this syncline, whence 

 the name for this shale formation. The Massanutten syncline crosses 

 Maryland in a southwest-northeast direction, occupying an area several 



