NO. 2 SMITHSONIAN EXPLORATIONS, I924 I5 



GEOLOGICAL FIELD-WORK IN TENNESSEE 



In the field season of 1924, R. S. Bassler, curator of paleontology, 

 U. S. National Museum, continued geologic work in Tennessee 

 commenced several years ago in cooperation with the Geological 

 Survey of Tennessee imder the direction of State Geologist Wilhur A. 

 Nelson. In previous seasons the geology and paleontology of the 

 Central Basin were studied, followed in 1923 by an investigation 

 of the eastern portion of the surrounding Highland Rim. In 1924 

 the Highland Rim work was carried northward to the Kentucky- 

 Tennessee boundary where an area of about 125 square miles com- 

 prised in the Lillydale quadrangle of the Cumberland River district 

 was mapped in detail. The primary object of this mapping was an 

 economic one for the geologic structure of the region gives it oil 

 possibilities. This area is far from railroad facilities and transporta- 

 tion is by the Cumberland River, when high enough, automobile some- 

 times, but most often by horseback. The method of transporting 

 gasoline is shown in figure 22. 



The Highland Rim of Tennessee is the plateau area averaging a 

 thousand feet elevation surrounding the Central Basin. It is usually 

 so flat that the underlying rocks are seldom exposed but in the Lilly- 

 dale quadrangle the Cumberland River and its tributaries have cut 

 so deeply into the Rim that the topography is very rough and the 

 strata are exposed at frequent intervals. Here the exposed strata 

 range in age from the Catheys (Trenton) limestone of the Middle 

 Ordovician to the Cypress sandstone of the Chester group near the 

 close of the Mississippian. The Catheys limestone and the succeeding 

 Leipers limestone of Upper Ordovician age are followed directly by 

 the Chattanooga black shale of Early Mississippian time, all Silurian 

 and Devonian strata being absent. The black shale formation is only 

 20 feet thick in this area but it is so widely distributed that the geo- 

 logic structure of the region is best determined by its outcrops. All 

 of the strata here are essentially horizontal, but by plotting the eleva- 

 tion above sea level of the base of this black shale from outcrop to 

 outcrop and connecting the places of equal elevation, thereby forming 

 a structure contour map, no less than 20 small but distinct dome-like 

 uplifts were discovered in this quadrangle alone. The formations 

 above and below the black shale exhibit this same structure but the 

 dip is usually so slight as to be almost imperceptible (fig. 23). Some 

 of the domes formed by the uplifted strata (fig. 24) are known to be 



