PRINCIPLES OF STRATIGRAPHIC CORRELATIONS 557 



thin and variable in thickness, the observed variations ranging between 

 35 and 100 feet. Above the latter, apparently again with a stratigraphic 

 hiatus between them, comes a series of fine-grained, thin-bedded lime- 

 stone, 400 feet to possibly 600 feet in thickness, that is correlated with 

 the Lowville. This determination is made chiefly on the basis of fossils, 

 the lower 50 feet containing fine examples of a fasciculated Tetradium, 

 referred provisionally to T. cellulosum, and the upper 200 feet Beatricea 

 gracilis. This is followed by typical Moccasin. Only the base of the 

 Moccasin is locally exposed, the remainder being covered by overthrust 

 Cambrian deposits. 



In the belt to the south of this, between Copper Eidge and Clinch 

 Mountain, the Holston rests unconformably on 84 feet of Mosheim 

 (lower Stones Eiver) limestone. About 660 feet of typical Holston 

 limestone, mostly heavy bedded marbles, is passed over before the first 

 appearance of the Ottosee bryozoan fauna which prevails in the succeed- 

 ing 470 feet. Though consisting mainly of shales and thin limestones, 

 the Ottosee here includes an 80-foot bed of massive pink marble. Above 

 the Ottosee the section at Thorn Hill exposes 150 feet of argillaceous 

 fine-grained limestone and shale not seen farther east in the same valley. 

 This is believed to represent a part of the Lowville in the War Ridge 

 belt. Some 200 feet or more of the overlying "Moccasin" probably also 

 is of Lowville age. Fossils are few and not very satisfactory, but what 

 there is of them is not opposed to this reference. 



Thus, by showing that the Holston succeeds the Stones Eiver ; that the 

 Athens shale follows the Holston ; that the Tellico lies between the Athens 

 and the Ottosee, and that the Lowville, in its fullest development, rests 

 on the Ottosee, the time value of the Pamelia-Lowville hiatus is estab- 

 lished, so far as it is represented by known sediments in the Appalachian 

 Valley. 



Demonstration by alternating northward and soutliward overlaps in 

 the Mississippi Valley. — The best ilhistrations of interfingoring of distal 

 edges of formations which transgressed from opposite directions arc those 

 of late Black Eiver and early Trenton ages which invaded the median 

 portions of the continent alternately from the north and the south, as de- 

 scribed on pages 367 to 371. Similarly alternating invasions occurred 

 during the Eichmondian and the Niagaran and probably also during the 

 late Devonian. The bearing on this principle of the interfingering Black 

 Eiver and Trenton formations referred to here is thought to be so obvious 

 that further discussion is unnecessary. Tt being established that the 

 formations overlap as described, probably none will question the infer- 



