﻿NO. I SMITHSONIAN EXPLORATIONS, I925 I3 



Fort Payne chert. The edges of the lower formation are clean 

 cut and show no signs of weathered products due to subaerial de- 

 composition, so that this seems a true case of submarine erosion. 



Viewed in most exposures, the Fort Payne chert of Keokuk age 

 appears to be conformable with the overlying Warsaw limestone 

 but that there was an actual time break, locally indicated by an 

 angular unconformity, is shown in figure 15. Here the lower for- 

 mation has been tilted at a slight angle and the edges of the strata 

 worn oft before the rocks of the newer formation were laid down 

 upon it. A still different structural type is illustrated in figure 16, 

 which shows the Fort Payne chert resting directly on the Early 

 Mississippian Chattanooga black shale, the unconformity between 

 the two being recorded elsewhere by 500 feet or more of shales and 

 limestones included in the Ridgetop and New Providence forma- 

 tions which were absent at this place. The particular interest of 

 this exposure is that the Chattanooga shale developed a sharply 

 defined channel in its top, either through fracturing or erosion, in 

 which the Fort Payne chert was deposited normally. The structure 

 of the Eastern Highland Rim near its junction with the Cumberland 

 Plateau was also studied. The Highland Rim forms a rolling up- 

 land averaging 1,200 feet in altitude and the Cumberland Plateau, 

 another marked upland area, 700 feet higher. In this part of the 

 State, the Highland Rim is traversed as shown in figure 17, by 

 low ridges which, as a rule, are due to structural features in the 

 underlying formations. These ridges, in most cases, are capped by 

 hard sandstone and indicate areas of slightly down folded strata 

 where the general level of erosion has not proceeded far enough 

 to entirely remove the resistant rock. 



Tennessee is uniquely situated for the study of stratigraphic 

 geology, and the State has long been classic ground. Starting with 

 the Blue Ridge system on the east and extending westward to the 

 Mississippi flood plain, it comprises many physiographic provinces 

 with the underlying strata embracing almost all the divisions of the 

 geologic column. Most of these strata are highly fossiliferous and 

 perhaps nowhere else can the development of life be studied to 

 better advantage. 



GEOLOGICAL FIELD-WORK IN CENTRAL NEW YORK 



The division of paleontology of the U. S. National Museum 

 contains great collections of Devonian fossils from the classic New 

 York areas, obtained years ago when the present methods of record- 



