4S8 C. SCHUCHERT PALEOGEOGRAPHY OF NORTH AMERICA 



Taconic revolution. — The period of this secular unrest was of long du- 

 ration, clearly beginning with the Trenton emergence and persisting to 

 the close of the Cincinnatic. The North Atlantic ocean was subsiding, and 

 as a result of this movement the older Paleozoic strata of eastern America 

 and western Europe were finally, by the tangential thrusts of the Atlantic, 

 thrown into folds upon which the succeeding deposits of these areas rest 

 discordantly.' 122 The movement was at first gentle, but culminated in the 

 widespread Richmond transgression, and at its completion showed a new 

 arrangement of lands and seas due to the decided secular changes previous 

 to the Siluric. The first noticeable effect of this developing revolution 

 may be seen in the turbulence of the oscillatory seas of Mohawkian time, 

 as described by Ulrich, and in the birth of the Cincinnati axis or parma, 

 never a marked feature of the Mississippian sea until the Siluric. The 

 axis at first appeared at the south as an island — Nashvillia — as early as 

 the Lowville, and persisted into earliest Trenton time. Subsequently it 

 was submerged, but reappeared in the Lorraine, and was greatly enlarged 

 during the Richmond. In the north its record is rather one of submer- 

 gence, but with the subsidence of the Richmond transgression the Cincin- 

 nati axis was ever afterwards a distinctive feature of the Mississippian 

 sea. With the rise of this low fold two other parmas appeared, having 

 similar trends, the eastern one being Alleghania and the western one 

 Kankakeia. The former apparently began with the Utica emergence, but 

 was more certainly visible in the Richmond transgression, while Kanka- 

 keia was not clearly seen as an axis until the Niagaran transgression of the 

 Siluric. The Pacific ocean also subsided, but its lateral effect was not so 

 continued and violent as that of the Atlantic, as no upturnings are here 

 known. However, somewhat later, when the Niagaran transgression was 

 at its maximum, it is evident that the Cordilleran and Mississippian seas 

 no longer had the free and wide open intercommunication of earlier 

 periods, but that in great part they were now separated by the extensive 

 land Siouxia, which was but the northern part of Columbia. 



The Taconic revolution of the North Atlantic is of great significance in 

 stratigraphy and paleontology, since in eastern North America the up- 

 turnings, according to Dana, 123 "extend all the way from the Saint Law- 

 rence valley to New York city, . . . through Virginia southwest- 



122 There is also at about this time marked movement in western Sonora, Mexico, as 

 neve the uppermost El Paso limestone (= Richmondian) rests discordantly upon other 

 limestones supposed to be of Beekmantown age. The Richmond fossils have been col- 

 lected by E. T. Dumble and sent to the writer. The structure of the region is described 

 by the former in Transactions of the American Institute of Mining Engineers, vol. 29, 

 1900. 



^ 3 Dana : Manual of Geology, 1895. pp. 387, 531. 



