556 E. O. ULRICH REVISION OF THE PALEOZOIC SYSTEMS 



Holston finally overlapped into the Newman trough. But the section 

 in Mulberry Valley shows that the faunas did not commingle. On these 

 grounds alone we would be justified in giving full weight to the evidence 

 of interrupted sedimentation there exhibited by the contact of the Hol- 

 ston wedge with the underlying Stones Eiver. 



But we can add something in corroboration of this faunal evidencti. 

 Thus, the basal member of the Chambersburg limestone in the vicinity 

 of Mercersburg, Pennsylvania, is over 200 feet thick and confidently 

 correlated with the Holston (see pages 325 to 328). It is sharply defined 

 from the upper Stones Eiver below and from the Lowville member of 

 the Chambersburg above. As these contacts are still unconformable, the 

 contention that the Holston at its maximum is younger than the Pamelia 

 Stones Eiver seems reasonably assured. The case so far and to its final 

 development is a clear illustration of the principle that the hiatus between 

 two important formations which invaded from the same oceanic basin 

 includes an interval during which invasion from another quarter occurred. 



It remains to be shown that the Pamelia-Lowville hiatus represents 

 not only the Holston but also the Athens, the Tellico, and the Ottosee. 

 The only feature of this problem that has not been established by positive 

 stratigraphic superposition is the relation of the Athens shale to the 

 Holston; and on this point we have faunal evidence that is satisfactory 

 if not conclusive, namely, the Murat limestone of west central Virginia 

 is an unquestionable extension of the Holston. At Lexington this lime- 

 stone is succeeded by a very striking fauna of which something like 80 

 species have been collected. This same fauna occurs at Blacksburg, Vir- 

 ginia, and at Pratts Ferry, Alabama, at the base of tlie Athens shale. 



In the Athens trough of east Tennessee, in which the Holston is ab- 

 sent, the Athens shale is followed by the Tellico sandstone. In both the 

 Athens trough and in the eastern part of the Knoxville trough the Otto- 

 see shale, which has been hitherto referred to the Sevier shale, rests on 

 the Tellico. Though not so thick as at Knoxville, Bulls Gap, and Athens, 

 the Ottosee is yet well and unmistakably developed in the two Ordovician 

 belts between Clinch Mountain and Clinch Eiver in Hawkins and Han- 

 cock counties. In both bands the Holston underlies the Ottosee, and over 

 that is the Lowville. The outcrops referred to are located in the northern 

 third of the Morristown quadrangle, and the formations have been 

 mapped by Arthur Keith as Holston marble, Chickamauga limestone, 

 and Moccasin limestone. 



In the band lying just north of War Eidge the Holston rests on a 

 very uneven floor of Knox dolomite. In thickness it varies from to 

 120 feet or more. The Ottosee, which overlies it unconformably, is also 



