112 The Lower Devonian Deposits of Maryland 



of Maryland. If it occupies like horizons in both areas then the Chonetes 

 jersey ensis fauna persisted longer in Maryland than in New Jersey, a 

 feature which may be due to the continuance of open-sea conditions for 

 a longer period in Maryland. Upon this supposition the upper part of 

 the Chonetes jerseyensis zone of Maryland may be synchronous with a part 

 of the Manlius of New Jersey. These conclusions, however, are not 

 assured and the true relations cannot be adequately determined until the 

 intervening area in Pennsylvania has been studied more critically. 



Following the deposition of the Decker Ferry and lower Keyser the 

 sea became more restricted as shown by the more argillaceous composition 

 of the overlying beds, the presence of numerous ostracods, and the greater 

 rarity of brachiopods in them. These features, however, are more marked 

 in New Jersey than in Maryland. 



The Eondout of New Jersey is an argillaceous limestone, one stratum 

 of which is a cement rock. Its fauna is peculiar to such sediments, con- 

 sisting almost exclusively of a few species of the genus Leperditia, all of 

 which are found in the Keyser of INIaryland, although they are not re- 

 stricted to one horizon. The most abundant species is Leperditia gigantea 

 which occurs at the Devil's Backbone 235-236 feet above the base of the 

 Keyser. 



The Eondout formation seems to have been a local deposit which had its 

 largest development in New York and thinned toward New Jersey. It 

 has not been recognized in Maryland. 



The Manlius of New Jersey, overlying the Eondout, is a nodular lime- 

 stone characterized by a Stromatopora reef and the abundance of Tentac- 

 ulites gyracantlius, Spirifer vamtxemi. Slropheodonta varidriata, and a 

 species of Leperditia identified as L. aJiu. The Favosites helderhergice 

 var. prcecedens zone of the Keyser of Maryland contains similar, though 

 more abundant, Stromatopora reefs at most localities. Tentaculites gyra- 

 canthus occurs in profusion between the Corriganville Stromatopora beds, 

 while Spirifer vanuxemi is represented by a variety that differs somewhat 

 from the typical form. The latter species is also found in the underlying 

 Chonetes jerseyensis zone where it more closely approaches the typical 

 form. A variety of Leperditia alia, known as L. altoides, is common in 

 certain of the upper beds of the Kevser member. Three of the four 



