140 THE CAMBRIAN AND ORDOVICIAN DEPOSITS OF MARYLAND 



*Rhinidictyd neglecta Ulrich 



Escharopora cf. ramosa 



*Prasopora insularis Ulrich 



*Hemiphragma irrasum (Ulrich) 



*Dianulites petropolitanus Dybowski 



Dalmanella testudinaria small variety 



*Dinorthis pectinella (Emmons) 



*Pianodema subaequata (Conrad) 



*Rafinesquina minnesotensis Winchell 



*Rafinesquina minnesotensis inquassa (Safdeson) 



Rafinesquina sp. 



Strophomena cf. 8. filitexta 



Plectambonites sp. 



Plectambonites pisum var. 



*Hebertella bellarugosa (Conrad) 



Triplecia (Cliftonia) simulatrix Bassler 



Leperditia cf. L. fabulites 



Pterygometopus cf. P. schmidti 



*Ampyx (Lonchodomas) normalis Billings 



The Echinospherites and Mdulites beds are well developed in all the 

 sections of this area, but the considerable thickening of the Christiania 

 bed north and also south of Maryland is a second interesting feature. 

 Finally, the occurrence of the Greencastle bed only in the area extending 

 from the Mason-Dixon line northeast to beyond Chambersburg shows 

 that local depressions in an area can receive sufficient sedimentation rep- 

 resenting a hiatus which would otherwise hardly be suspected. In these 

 various sections the Upper Stones River below and the Sinuites zone at the 

 base of the Martinsburg above, form two datum planes which are recog- 

 nized without difficulty. 



Nidulites- Bed. The Nidulites bed is the most conspicuous division of 

 the Chambersburg in Maryland and forms the main part of the outcrops 

 of the formation both east and west of the Martinsburg shale belt. The 

 heaviest limestones of the formation are included in this bed which, as a 

 rule, tends to weather in smooth, rounded outcrops like the underlying 

 massive limestones of the Stones River and Beekmantown formations, 

 instead of the usual cobbly layers. Cobbly layers do occur in this bed and 

 their weathered outcrops have much the appearance of the underlying 

 Echinospherites bed. In such cases a brief search will reveal the occur- 



