PRINCIPLES OF STRATIGRAPHIC CORRELATIONS 545 



middle Stones Eiver sea on the west from the Lenoir limestone bay on 

 the east, Next the Lenoir bay was entirely drained and subsequent late 

 Stones Eiver deposition confined to areas west of the Clinton trough. 

 The general emergence which terminated the Stones Eiver was followed 

 by the Holston submergence of the valley troughs. To the south of the 

 Knoxville parallel the Holston marble is confined to the Knoxville 

 troughs, but northward from this city a thin crystalline limestone, pro- 

 visionally referred to the Holston (it may belong to the Ottosee), trans- 

 gresses these boundaries and overlaps as far as the Newman trough in 

 Hancock County. As shown in the accompanying table, the succeeding 

 Ordovician seas shifted back and forth across the valley, but the shifting 

 seems always to be in accord with a definite plan. Additional information 

 respecting the migration of Ordovician seas in the Appalachian Valley 

 is brought out in the discussion of principles 17 and 18. 



Judging from the known and inferred extent of post-Clinton Niagaran 

 seas in southeastern North America, it is thought quite improbable that 

 any marine deposit of this age will ever be found in the Appalachian 

 Valley from Lake Champlain to Alabama. Under this belief the Sneed- 

 ville limestone in Hancock County, Tennessee, a formation long ago 

 referred to the Niagaran by Safford, was investigated and shown to 

 be post-Niagaran — probably Manlius — in age. Also, the beds in Mary- 

 land, now known as the McKenzie formation, which Schuchert in 1903 

 and others since then have referred to the Niagaran, were studied recently 

 and proved to be of Cayugan age. 



On the other hand formations have been recognized in areas where 

 their presence was originally suggested on theoretic grounds. For in- 

 stance, everything seemed to support the belief that the upper Stones 

 Eiver sea extended northward into north central New York. The valid- 

 ity of the suggestion is now established, Cushing (1908) having de- 

 scribed and proposed the name Pamelia for the upper Stones Eiver lime- 

 stone in that State. 



Many such verified predictions based on inferred probabilities respect- 

 ing the geographic pattern of Paleozoic continental seas might be cited, 

 but those mentioned, it is believed, will suffice to illustrate the principle. 

 The matter of rhythm in recurrence of geological phenomena is rather 

 fully discussed in Part III (pages 599 to 607). 



(16) Correlations implying complete emergence of continents at fre- 

 quent intervals. — General emergence of continents to approximately their 

 present and occasionally even greater dimensions is believed to have 

 occurred at the close of each period and probably also at the close of 



