THE CENTRAL BASIN OF TENNESSEE. 83 



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

 Valley, and covered the gi-eater part of the centre of Xorth America. 

 The whole territory fi'om the border of ZS orth Carolina wa.s under 

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

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

 the sea bottom, the Owee conglomerates, Chilhow^e sandstones, the 

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

 associated Nashville 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 Nashville or Hudson River period there was a 

 period of gi-eat disturbance which resultei in the upheaval of a long 

 line of dome-like structures extending from Alaljamn in tlie south- 

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

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

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

 and pa.sses into Indiana. The ridge thus thrown up rose higher 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 tlian in the other or longitu'linal 

 directions, the two dips in the I'egion of the Basin being southea.st and 

 noi-thwest 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 HelderVjerg rocks are to be found surrounding the various 

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

 as islands in the Lower Silurian sea. 



The district now occupied by the Central Ba.sin was the site of one 

 of the.se domes, or islands with an area of over 150 miles in length, 

 extending from the northern pait of Alabama to the centre of 

 Kentucky and from a few miles west of the Sequachee Yalley 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. 



