Maryland Geological Survey 



99 



The lower faunal zone is here termed the Chonetes jerseyensis zone. 

 It is about 110 feet thick a.nd is characterized by the presence of Chonetes 

 jerseyensis and associated species. The upper zone is termed the Favosites 

 helderhergice var. pi-cecedens zone from the abundance of that coral in it. 

 The fossils found in the latter zone differ to a large extent from those of 

 the Chonetes jerseyensis zone. 



A conspicuous feature of the Keyser member is the existence in it of at 

 least five thick reefs of corals and stromatoporoids. It was long sup- 

 posed that but two such reefs were recognizable in Maryland, both of 

 which are exposed at the Devil's Backbone. Further study, liowcver, has 

 shown the presence of similar reefs at other horizons. These reefs are of 

 wide extent. They are usually very resistant to weathering and stand out 

 as massive ledges on the hillsides, the weathered stromatoporoids present- 

 ing a singular curly and knotted appearance. 



Both the Chonetes jerseyensis and Favosites helderhergice var. prcecedens 

 zones may be further divided into a number of subzones, each of which is 

 characterized by some diagnostic feature as shown in the following table : 



Keyser member. 



Favosites helderbergiffi var. 

 preecedens zone. 



Chonetes jerseyensis zone. 



Leperditia subzone. 



Corriganville Upper Stromato- 

 pora reef. 



Tentaculites gyracanthus sub- 

 zone. 



Corriganville Lower Stromato- 

 pora reef. 



RensselEeria mutabilis sub- 

 zone. 



Keyser coral reef. 



Bryozoan subzone. 



Gypidula coeymanensis var. 

 prognostica subzone. 



Spirifer modestus-cystid sub- 

 zone. 



Rawlings Stromatopora reef. 



Cladopora rectilineata sub- 

 zone. 



Rhynchospira subzone. 



Warrior Mountain coral reef. 



