THE CENTRAL BASIN OF TENNESSEE. 83 



which extended from the Gulf of Mexico, up through the Mississippi 

 Valley, and covered the greater part of the centre of North A merica. 

 The whole territory from the border of North Carolina was under 

 water. In a comparatively shallow sea, and under varying conditions 

 of alternately clear and muddy water, and after various oscillations of 

 the sea bottom, the Owee conglomerates, Chilhowee sandstones, the 

 Knox shales and dolomites, and the Trenton limestones, with the 

 associated ISTashville shales and limestones were laid down. This 

 closed the Lower Silurian Age so far as this part of the continent 

 was concerned. 



At the close of the ISTashville or Hudson River period there was a 

 period of great disturbance which resulted in the upheaval of a loner 

 line of dome-like structures extending from Alabama in the south- 

 west to Ohio in the north-east, and traversing the States of Tennessee 

 and Kentucky. From South-western Ohio this same upheaval, known 

 in Ohio as the Cincinnatti axis, takes a bend round to the north-west, 

 and passes into Indiana. The ridge thus thrown up rose hio-her in 

 some parts than in others with the dip of the strata quaquaversal or 

 radiating in eveiy direction, but in general having a greater angle of 

 dip south-easterly or north-westerly than in the other or longitudinal 

 directions, the two dips in the region of the Basin being southeast and 

 northwest for transverse, and for longitudinal directions northeast and> 

 southwest. It is due to this quaquaversal condition of the beds that, 

 the elevation is of a dome-like structure, and it is also due to the 

 variations in the dip in the longitudinal section that the Niagara and: 

 Lower Helderberg rocks are to be found surrounding the various, 

 isolated portions of these ridges, or what may be better regarded 

 as islands in the Lower Silurian sea. 



The district now occupied by the Central Basin was the site of one 

 of these domes, or islands with an area of over 1.50 miles in lenc^th, 

 extending from the northern part of Alabama to the centre of 

 Kentucky and from a few miles west of the Sequachee Valley to a 

 circularly drawn line extending from Macon County on the north, to^ 

 Lincoln County on the south, as its Western boundary. The centre- 

 of this Silurian island was according to Professor Safford a few miles 

 to the" south-east of Murfreesboro in Rutherford County, near the 

 eastern escarpment and now almost the lowest spot in the whole basin.. 



