353 On the Silurian Basin of Middle Tennessee. 



possession of tidal registers which have been kept during the 

 progress of the local surveys made of harbors on the coast of the 

 Gulf of Mexico. The tidal observations of Major Bache, U. S. 



Topographical EngineerSj at Key West and the Tortugas, are 



the most complete of this series, and show, as a general phenom- 

 enon, the prevalence of the semi-diurnal wave at that point. I 

 have not yet had the opportunity to examine fully these results; 

 which are however under discussion. 



Art. XXXVL— TAe Silurian Basin of Middle Tennessee, with 

 notices of the Strata surrounding it ; by James M. Safford, 

 A.M., Prof, of Chemistry and Geology, Cumberland Univ., 

 Lebanon, Tenn., with a plate. 



1. The rocks of Middle Tennessee, west of the Cumberland 

 Mountains, belong, for the most part; to strata below the Pen- 



tremital carboniferous limestones. 



•^ 



fi 



roups 



) 



The First and Second, commencing with the lowest, comprise 

 the '' Blue limestones'' of western geologists. 



The Third includes the gray limestone of the Harpeth and 

 Tennessee rivers. 



The Fourth^ the well known "^ Black slate." 



The Fifth and uppermost, the '^ siliceous stratum" of Dr. 

 Troost — a heavy group, often including limestone, but well 

 marked everywhere by its siliceous character. 



3. The strata of these groups, originally, formed a slightly 

 elevated dome, the denuded summit of which is in Rutherford 

 county. Here the lowest of the rocks under review are visible. 

 From this point the dip eastward is very slight ; towards the Illi- 

 nois coal-field, however, it is considerable, being from four to five 

 hundred feet in sixty miles, and sufficient to bring the uppermost 

 group down to the level of the Cumberland river, in Montgomery 

 county. Towards the south and west, the dip of the "blue 

 limestones" is greater than that of the " black slate" and the 

 siliceous group above, thus making room for the Harpeth and 

 Tennessee river group. 



4. The groups enumerated above have been denuded in such 

 a way as to form a basin^ its outlines more or less obscured by 

 "spurs," hills, &c., though, upon the whole, well defined ; it is 

 of an oval figure, about one hundred miles long and fifty or sixty 

 broad, and runs somewhat obliquely across the state. (See map 

 Plate 7.) I have denominated it the Silurian basin, since^ the 

 rocks of the entire area are of Silurian age, the *'blue lime- 

 stones," or groups first and second, being the surface-rock of the 

 level and rolling lands constitutins: the bottom of the basin. 



) 



