MARYLAND GEOLOGICAL SURVEY 117 



been noted, only two of which are sufficiently preserved for specific 

 description. These are Acidaspis ulrichi and Strophomena stosei, two 

 new species and an undetermined species each of the genera Reteocrinus ?, 

 Cameroceras and Isotelus. The prime interest of this fauna, like that 

 of the underlying Beekmantown, is in its occurrence east of the Blue 

 Ridge. This particular association of species is also noteworthy because 

 neither the fauna itself nor the beds containing it can be correlated 

 directly with any Appalachian Valley formation. However, the fauna 

 suggests a Chazyan or early Mohawkian age with the possibility more in 

 favor of the former. 



THE STONES RIVER LIMESTONE 



The purest limestones of the Shenandoah series are contained in the 

 strata occurring between the underlying finely laminated pure and 

 magnesian Beekmantown formation and the overlying argillaceous 

 nodular Chambersburg limestone of Black River age. These pure lime- 

 stones are correlated on lithologic, stratigraphic, and paleontologic 

 grounds with the Stones River group or formation of the Central Basin 

 of Tennessee. In Maryland the Stones River limestone rests unconform- 

 ably upon the Beekmantown, the uneven contact being well marked by an 

 extensive development of secondarily silicified chert known as " cauli- 

 flower " chert. 



The Stones River was named and defined as a distinct group in 1855 

 by Safford, who based it on the limestones outcropping along the Stones 

 River in the vicinity of Murfreesboro, Tennessee. The group includes 

 the lowest rocks appearing at the surface in the Nashville dome of the 

 Cincinnati axis. Safford, in his " Geology of Tennessee" (1869), aban- 

 doned the term under the misapprehension that the Stones River rocks 

 were equivalent to the Trenton of New York. Winchell and Ulrich, in 

 1897, revived the name, and later Ulrich and Hayes, in the description 

 of the Columbia quadrangle of the IT. S. Geological Survey, more com- 

 pletely defined the group. 



GENERAL SECTIONS. As recognized to-day the Stones River group in 

 its type area in Central Tennessee includes the following formations : 



