STRAND-LINE DISPLACEMENTS 487 



shales and entombing an Atlantic nektonic-pelagic fauna quite foreign to 

 the Mississippian sea. In the early stages the Utica sea covered about 10 

 per cent of Xorth America, then gradually became smaller, and during the 

 later portion of this time the tide turned, the strand-line slowly becoming 

 positive and bringing back the normal faunas for the Mississippian sea, in 

 this case the Eden and Lorraine. 



Cincinnatic period 121 — Eichmond transgression (plates 61, 62). — Dur- 

 ing Lorraine or Maysville time the strand was not very positive, as the sea 

 was withdrawn more and more from Xew York. In the southwestern part 

 of Ohio the latest L^tica and Eden were continuous into the Lorraine, but 

 at this time communication was again established with the southern Appa- 

 lachian trough, thus introducing the Gulf faunas. In the Cincinnati 

 region the Lorraine passed not quite uninterruptedly into the Arnheim 

 stage of the Lower Eichmond, the sea being then probably more to the 

 east along the deeper water off the axis. Slowly the Taconic revolution 

 dissipated the Mississippian sea to the northeast of the Cincinnati axis, 

 and finally in the later Eichmond the inundation again became general 

 west of the axis, almost duplicating the Trenton transgression. The fig- 

 ures are as follows : 



North America. United States. 



Trenton transgression 57 per cent Gl per cent 



Richmond " 40 " " 44 " " 



The Utica emergence left the North American continent with itis pre- 

 vious attitude, so that the Eichmond transgression laid down its deposits 

 in perfect concordance with the older formations. This sea was also an 

 oscillatory one, the pulsations being best recorded in the Mississippi val- 

 ley. It will be some years, however, before ITlrich can describe the various 

 faunules which together make up the Eichmond series. On Anticosti 

 the connecting record is complete, and its interpretation is now being 

 attempted at Yale University; hence it is hoped that the line which sepa- 

 rates the Cincinnatic from the Si 1 uric may soon be located. The Eich- 

 mond faunas have northern European affiliations, but because of the 

 nearly universal and broadly intercommunicating continental seas it is 

 expected that southern Poseidon, Pacific, and Arctic elements will sooner 

 or later come to light. 



The Eichmond transgression was closed by the Taconic revolution, 

 during which time there was great subsidence of the seas. The final 

 waters were local in situation, being possibly of the nature of attracted 

 seas, and their faunas more and more assumed a Siluric aspect. 



121 Cincinnatian or Upper Ordovician of geologists. 

 XLIV — Br-r.L. Geol. Sec, Am.. Vol. 20. 1908 



