10 RESOURCES OF TENNESSEE. 



exposed anywhere within the Central Basin, is a formation 

 called the Knox dolomite. This formation extends eastward 

 beneath the Cumberland Plateau and is the surface rock in a 

 large part of the Valley of East Tennessee, having received its 

 name from Knox County. It is composed of limestone, dolo- 

 mite, and a small amount of sandstone, and in East Tennessee 

 reaches a thickness of 3500 feet. Its thickness in the Central 

 Basin is not known, but that it occurs there is shown from its 

 appearance in Wells Creek Basin 40 miles northwest of the 

 Central Basin, in the southwestern part of Stewart County. It 

 is not probable that the thickness of this formation in Middle 

 Tennessee is as great as in East Tennessee. 



With the exception of the Pierce formation, practically all 

 the rocks of the Central Basin are limestone, and even this 

 formation is itself composed of limestone and limey shale. 



Structure of the Central Basin. If the rocks of the Central 

 Basin were level, only the upper formations of those named 

 above would show at the surface; but instead, the Basin is a 

 great arch, or rather a dome, of slight elevation. In general, 

 the arching does not end where the rocks pass under the High- 

 land Rim, but continues a greater or less distance beyond. The 

 figure herewith will give a general idea of the structure. 



The highest part of the dome occurs in the vicinity of Mur- 

 freesboro, Rutherford County; and here, all the upper forma- 

 tions have been removed down to the Ridley limestone, the 

 Pierce shale, and the Murfreesboro limestone. This removal 

 of the rocks is a part of the general one that has taken place 

 all over the Central Basin, and to this the basin owes its exist- 

 ence. The process of removal has been mainly by solution. The 

 Highland Rim has escaped removal, because the rocks compos- 

 ing it are more siliceous than those of the Central Basin and 

 for this reason have resisted the solution that took place in the 

 comparatively easily soluble limestones of the latter area. The 

 agent of solution was the water that fell as rain, and flowed 

 off over the surface and through the rocks. 



As the rock beds were arched up higher in the vicinity of 

 Murfreesboro than elsewhere, it will be seen that the removal 

 of the rocks from the area would bring the lower and older 



