306 CEMENT MATERIALS AND INDUSTRY. [bull. 2 
These Trenton formations, though consisting almost entirely of lim 
stone, still vary greatly from place to place in their lithologic charj 
ters. The Bigby limestone, for instance, is granular and phosphat 
on the west side of the basin. Both of these peculiarities are lost 
tracing the formation around the northern and southern sides to t 
eastern border. Here a large part of the formation, which has. mo 
over, increased in thickness, consists of compact earthy limestones. 
The Trenton limestones in the counties bordering the Cumbcrla 
River, if the present local scarcity of fuel is not prohibitive, are pad 
ticularly promising materials. Coal was formerly boated down fron 
eastern Kentucky mines, and these shipments might be resumed 
there was sufficient reason. At present only points in the vicinity q 
Nashville and Carthage have access to coal brought in by railroa 
At both of these places, however, there is such a variety of limesto 
and shales that it is scarcely to be doubted that abundant materi 
affording the proper mixture are* available at either. 
Leipers formation. — This formation consists, as a rule, of interbedd 
shales and apparently nonmagnesian, thin, knott} T limestones. It varie 
considerably in composition from place to place, and even in the saJ 
outcrop, and on this account is not deemed so promising as most I 
the underlying Trenton and Stones River formations. The Leiper 
outcrops chiefly in the slopes of the highland rim. Stratigraphicallili 
it is equivalent to the formation in the hills about Cincinnati, Ohio 
SILURIAN LIMESTONES. 
The Silurian rocks of Tennessee embrace three limestone f ormatioi 
containing beds sufficiently low in magnesia to be considered availab 
as Portland cement materials, viz, the Clifton limestone (Niagara 
the Linden limestone (Helderberg) of middle and western Tennesse 
and the Sneedville or Hancock limestone (Helderberg) of northeaster 
Tennessee. The Clifton and Linden limestones outcrop chiefly aloir 
the Tennessee River, and both, the Linden especially, contain intei' 
stratified beds of shale. Locally, the Clifton contains beds that ar 
more or less highly argillaceous. These argillaceous limestones occo 
principally in the lower part of the formation. Locally, as in tt 
bluff's opposite Centerville, in Hickman County, they may affor 
material suitable for so-called natural Portland cements. 
MISSISSIPPIAN LIMESTONES. 
Nonmagnesian limestones occur in three Mississippian formations i 
Tennessee. The lowest of these is the Tullahoma formation, in whic 
the limestones are prevailingly very siliceous and cherty, and for th 
aGeologic Atlas U. S., folio 95, U. S. Geol. Survey, 1903, pp. 1-2. 
