530 C. SCHUCHERT PALEOGEOGRAPHY OF NORTH AMERICA 



an area intermittently connected with England and the Atlantic. At this 

 time the Atlantic fauna still had its own characteristics and was again 

 marked by graptolites of the Normanskill, Magog, and CUmacograptus 

 ■caudatus zones, common to eastern America and Great Britain. 



Late in the Trenton the transgression by that name began to disappear, 

 first in the Arctic region, then in the Pacific and Gulf areas, culminating 

 with the Utica in the Utica emergence. This withdrawal of the sea was so 

 widespread, while the deposits that were subsequently laid down on these 

 lowest Trenton strata are usually so absolutely conformable, that one is 

 forced to the conclusion that some oceanic area had been deepened, thus 

 causing the waters to flow off the continent. During this retreat of the 

 sea the first evidence of those peculiar heavily armored fishes belonging to 

 the Ostracoderms appears in cleanly washed beach sands and less abun- 

 dantly in dolomites at three widely separated places in Colorado and 

 Wyoming. They are now all fragmentary and seem to have been washed 

 into the sea by the rivers. From this can it be inferred that during some 

 earlier inundation the marine ancestors of these fishes were retained upon 

 the land in relict seas, and under the stress of evanescent waters became 

 modified into the armored double-breathing animals that gave rise later 

 to the true fishes ? Such being the interpretation, the marine fishes must 

 then have been derived from land fishes, as suggested by Chamberlin and 

 Salisbury. 



Cincinnatic Period (new) 



(Upper Ordovician or Cincinnatian of authors) 



See plates 61 and 62, and pages 487-489 



See Ulricas paper for the detailed discussion of this system. 

 Type area: Southwestern Ohio and southeastern Indiana. 152 



Table of Cincinnatic Formations 

 Siluric. 



Elkhorn zone, 50 feet. 



Whitewater zone, 75 feet. 



Saluda zone, 5-23 feet. Thebes ~\ 



Liberty zone, 30-50 feet. Maquoketa. j- Mississippi valley. 



Waynesville zone, 00-80 feet. Fernvale. . . j 



Arnheim zone, 80 feet. 

 f Mount Auburn zone, 20 feet. 

 I Corryville zone, 60 feet. 



Maysvillian -{ Bellevue zone, 20 feet. 



I Fairmount zone, 80 feet. . ) T , T • *-■«- at i 



L Mount Hope zone, 50 feet. } In P art ' Lorraine of INew York. 



Kichmondian . 



152 Nickles : American Geologist, vol. 32, 1903, pp. 202-218. Journal of the Cincinnati 

 Society of Natural History, vol. 20, 1902, pp. 49-100. Cumings : Thirty-second Annual 

 Report of the Department of Geology and Natural Resources of Indiana, 1908, pp. 607- 

 1189. 



