MURPHREE'S VALLEY; GEOLOGICAL FORMATIONS. 25 



SILURIAN. 



1. The Clinton or Red Mountain. Thi, with its varied 

 strata and included iron beds, will be hereafter described in 

 detail. It is generally regarded as. the lower member of the 

 Niagara period, and is the only representative of the upper 

 Silurian in this region. Its average thickness in Murphree's 

 Valley may be given at about 150 feet. 



2. Trenton and Chazy, Pelham. The Trenton is conspic- 

 uous and easily identified, wholly composed of limestone, 

 over 250 feet in vertical thickness. At its base is a regular 

 stratum, 20 to 50 feet thick, ot li^ht colored compact mag- 

 nesian limestones. These lie conformably on the stratified 

 quartzose rocks, of which the next thousand feet are mainly 

 composed. Near the top of this great quartzose or chert 

 member there is a peculiar conglomerate, and two thin lime- 

 stone beds ; they are by some geologists considered as repre- 

 senting the Chazy formation. The fossils however, of which 

 there are many, have been considered by paleontologists as 

 belonging to an earlier age. A very characteristic form of 

 this horizon is Maclurea magna. 



3. Knox Dolomite. This is in many respects the most im- 

 portant of the older geological formations. It is over 1,000 

 feet in thickness, and forms the surface over the greater part 

 of the anticlinal valleys of the state. Some of the most im- 

 portant of the beds of limonite or brown iron ore lie upon 

 it. In its lithological characters this formation in Alabama 

 is identical with the Knox Dolomite of Tennessee, as de- 

 scribed by Dr. Saiford. In its lower part it consists of lime- 

 stones and dolomites of blue and gray colors, often especially 

 in the lowermost beds, interstratified with shale. The dis- 

 integration of these beds gives rise to the fertile red lands 

 which form the best farming areas of this and the other 

 valleys. It is difficult to draw a sharp line of distinction be- 

 tween this lower part of the Knox Dolomite and the up- 

 per beds of the underlying Cambrian. 



The upper part of the Knox Dolomite consists of gray 



