102 THE CAMBRIAN AND ORDOVICIAN DEPOSITS OF MARYLAND 



railroad cut about three-fourths of a mile east of Charlton, Md. Here 

 deep weathering and decomposition of the steeply dipping limestone strata 

 has removed their calcareous matter and left only residual clays with 

 the chert clearly marking its position. The abundance of chert and 

 silicified Cryptozoon heads formed in the weathering of this zone is well 

 attested by the frequent piles of chert collected along the roadways. 



Immediately following this cherty zone with Cryptozoon are 300 feet 

 of dove and pink fine-grained pure limestone, of which a considerable 

 portion can be called marble. These marble beds are well shown in several 

 railroad cuts around Hagerstown. Fossils are rare in these strata, but an 

 occasional layer shows traces of species found also in the underlying beds 

 holding Cryptozoon steeli. This zone ends with 275 feet of fine-grained, 

 nearly pure limestone with occasional beds of magnesian limestone and 

 several layers of porous chert. 



The platy chert, weathering out of the limestone of the Cryptozoon steeli 

 zone is common at all outcrops of the zone, but is so abundant in the 

 western half of the valley that it occasions a distinct row of hills marking 

 the line of outcrop. This topographic feature and the numerous masses 

 of Cryptozoon associated with the chert cause this portion of the Beekman- 

 town to be easily recognized. The following species have been found either 

 associated with Cryptozoon steeli or in strata underlying it, but still 

 included in this division : 



Fossils of Cryptozoon steeli Zone 



Cryptozoon steeli Seely 

 Rhabdaria fragilis (Billings) 

 Tetradium simplex new species 

 Syntrophia lateralis (Whitfield) 

 Maclurites affinis (Billings) 

 Eccyliopterus triangulus (Whitfield) 

 Ophileta compacta Salter 

 Hystricurus conicus (Billings) 



At the very base of this zone two interesting fossils have been found 

 associated with the usual gastropods. These are the sponge-like organism 

 Rhabdaria fragilis Billings and Tetradium simplex, a new species of coral 

 of particular interest in being the oldest known undoubted coral. 



