306 E. O. ULRICH REVISION OF THE PALEOZOIC SYSTEMS 



2 feet — where it is succeeded by the Maquoketa than it is where the 

 Mississippian rests on it. 



It has not seemed possible to decide whether the exceedingly soft 

 Maquoketa shale originally extended over all the known Fernvale areas. 

 In my opinion it did not; but the point is not of material consequence. 

 The astounding fact remains that erosion during an emergence extending 

 through nearly the whole of two periods, the Silurian and Devonian, 

 failed to remove a bed of limestone less than 5 feet thick ! And this is 

 not a unique case. The Mississippi Valley and other areas of Paleozoic 

 interior seas are full of such instances. The Fernvale one is used to 

 illustrate the proposition of exceedingly slight erosion only because it is 

 so easily and positively demonstrable. 



LATE RICHMOND SUBMERGENCE 



The extraordinary extent of the late Eichmond deposits affords even 

 more instructive features than does the early Eichmond Fernvale lime- 

 stone. This late Eichmond horizon, so far as known, never exceeds 25 

 feet in thickness. It is characterized by an association of corals, bryozoa, 

 and brachiopods that may be recognized instantly. Because of the pres- 

 ence of the genera Halysites, Heliolites, Calopoeoia, and Favosites it has 

 frequently been identified as Niagaran. Hall, relying more on the Ordo- 

 vician aspect of some of its brachiopods, referred to it as a Hudson fauna. 

 This fauna and presumably stratigraphic horizon has been found on 

 Saint Josephs Island in Lake Huron, in the Mississippi Valley to the 

 north and south of Saint Louis, in the Big Horn Mountains of Wyoming, 

 in Colorado, in Utah, in Manitoba, in the Eureka district of Nevada, in 

 New Mexico, and in the Franklin Mountains near El Paso, Texas. Some 

 of the corals and the most peculiar of the bryozoa occur in the upper 

 Lyckholm of the Baltic section; also in the lower part of the Anticosti 

 group in the Bay of Saint Lawrence. Apparently the same fauna has 

 been found by Mr. Kindle in the Seward peninsula of Alaska. There is 

 some evidence tending to show the presence of the Atlantic phase of this 

 fauna near the top of the Eichmond in Kentucky and Indiana, but on 

 this point I prefer not to take a definite stand. 



At Thebes, in southern Illinois, the bed holding this Galopcecia fauna 

 rests on the eroded surface of the Girardeau limestone; in Lincoln 

 County, Missouri, where it is found in the Noix oolite, on Maquoketa 

 shale ; in Lake Huron, on lower Trenton ; in Manitoba, Wyoming, Colo- 

 rado, Utah, Nevada, New Mexico, and Texas, locally on earlier Eich- 

 mond deposits, but more pommonly on typical Galena. Clastic matter 

 occurs in the bed only as calcareous mud seams between layers of pure 



