SILURIAN. 235 



Foerste ^''"* also discusses the limestones of western Tennessee, in part as 

 follows : 



In southern Indiana the Silurian strata are divided into the following beds, named in 

 descending order : 



Louisville limestone. 

 Waldron shaly clay. 

 Laurel limestone. 

 Osgood shaly clay. 

 Clinton limestone. 



Southward, along the western flank of the Cincinnati geanticline, the equivalents of_ 

 these beds may be traced with varying success even as far as northern Alabama. * * • * 

 Very Uttle change is shown in the lithological characteristics of any of these subdivisions between 

 southern Indiana and northern Tennessee. North and south of this area, however, the Osgood 

 bed rapidly becomes more calcareous and is changed from a shaly clay to a soft limestone, 

 weathering more readily than the Clinton limestone below or the Laurel limestone above. 

 The Waldron bed also becomes calcareous northward and is replaced by limestone in central 

 Indiana. Southward it may be traced as far as northern Alabama, but in central and southern 

 Tennessee it is only 3 to 4 feet thick, and along the middle part of the bed the clay is replaced 

 by a layer of limestone 6 to 10 inches thick. Both northward in Indiana and southward in 

 Tennessee the Waldron bed maintains its characteristics as a shaly clay farther than the 

 Osgood bed. 



The thickest sections of the Osgood bed are found in central Kentucky. * * * At Bled- 

 soe in northern Tennessee, the Osgood bed consists chiefly of soft clay. * * * Jq central 

 and southern Tennessee the Osgood bed consists of rather thin bedded limestones weathering 

 back more readily than the Laurel bed above and the Clinton bed beneath. Here its identity 

 can often be estabhshed only with difficulty. The Waldron bed maintains its character as a 

 shaly clay horizon much farther southward than the Osgood bed. It is tjrpically developed 

 along the Harpeth River near Newsom. At this locahty it contains a large part of the fauna 

 characteristic of this horizon at Waldron, Ind. In central and southern Tennessee a thin bed of 

 limestone, 6 to 10 inches thick, replaces the clay along the middle of the bed. * * * 



Along the western flank of the Cincinnati geanticline, in southern Indiana, Kentucky, and 

 Tennessee, the name Louisville bed has been given to the Silurian rocks overlying the Waldron 

 bed. In the Tennessee River valley, in western Tennessee, the Silurian section overlying the 

 Waldron bed is so thick that it has been found necessary to subdivide it. 



At the base is a series of limestones, varying from 30 to 45 feet in thickness, to which the 

 name Lego limestone is here given. Stratigraphically this bed occupies the same position as the 

 Louisville bed. Its paleo'ntological equivalence, however, has not yet been determined, owing 

 to the small number of fossils so far obtained in the Lego limestone. Overlying the Lego Hme- 

 stone is a series of red clays, 30 to 45 feet thick, to which the name Dixon clay is given. This 

 clay has so far proved comparatively unfossiliferous. * * * Above the Dixon red clay is a 

 section of white limestones and clays, exceeding 100 feet in thickness. This section is often richly 

 fossiliferous. * * * To this section overlying the Dixon red clay the name Brownsport bed is 

 here given. 



Lithologically the limestones forming the middle and lower part of the Lego bed often 

 resemble those forming the Laurel bed so much that, in the failure to identify the Waldron 

 horizon, it is impossible to distinguish the same. 



Foerste ^*°^ gives the early and later nomenclature applied to the strata and 

 the equivalence of the limestones to other beds. The Clifton formation (the 

 Meniscus limestone of Safford) includes all the Niagaran strata present in western 

 Tennessee. 



