540 C. SCHUCHERT PALEOGEOGRAPHY OF XORTH AMERICA 



Montgomery limestone. 159 On the lower Ramparts of the Porcupine, in 

 Alaska, Kindle 160 reports a dolomite series estimated at 2,500 feet in 

 thickness. The fossils listed indicate Lower Niagaran time. In south- 

 eastern Alaska there is even a thicker series of limestones, with additional 

 argillites that range up into the Guelph. 161 



Devonic Period 

 See plates 72-77, and pages 491-493 



It has been seen that the Siluric closed with most of the North Ameri- 

 can continent emerged. This condition continued with slight marine 

 oscillations throughout the Helderbergian and Oriskanian epochs. Dur- 

 ing these intervals the continent was never inundated more than 9 per cent 

 and the United States 14 per cent. The faunas prophetic of the Devonic 

 appeared in the earliest of these invasions — that is, the Coeymans — and 

 rapidly took on the aspect clearly seen in the later Oriskanian. 



Late in Oriskanian time the Decewville formation of cleanly washed 

 beach sands, with Atlantic faunas, spread westward through New York 

 into Ontario, and at the same time the Gulf of Mexico embayment, with 

 Brazilian faunas, progressed northward along the western side of the Cin- 

 cinnati axis. 



This furnished the introduction of the fourth decided Paleozoic inun- 

 dation, which attained its climax in the late Hamilton, and persisted, 

 with a little emergence toward the close of the Chemung, into the Kinder- 

 hookian. In areal extent this submergence was identical with that of the 

 Siluric. The Gulf faunas of Onondaga, time are of a more decided warm 

 clear water sea, apparently unrepresented in South America. This sea 

 brought the second widespread coral reefs into the interior region. These 

 reefs are best developed at Louisville, Kentucky ; Columbus, Ohio ; Onta- 

 rio, and western New York, spreading north into the Hudson Bay region 

 and eastward across the Taconics into the Connecticut trough and the 

 Saint Lawrence sea. Thus the Onondaga is made up of two faunal ele- 

 ments — a larger and dominating biota derived from the south, and a 

 smaller, not especially different element, but well represented by cephalo- 

 pods, from the North Atlantic, together with many Oriskanian descend- 

 ants and some hold-overs. 



In the area of the Great Basin there is another series of faunas begin- 

 ning with Helderbergian time, and apparently persisting unbroken into 





159 Diller: Bull. 353, U. S. Geological Survey, 190S, p. 16. 



160 Kindle : Bull. Geological Society of America, vol. 19, 1908. 



161 Kindle : Journal of Geology, vol. 15, 1907. 



