PRINCIPLES OF STRATIGRAPHIC CORRELATIONS 539 



Considering the frequency of proved cases like the foregoing, it may 

 well be questioned if it is not more reasonable to assume difference in 

 age rather than contemporaneity of formations in neighboring troughs 

 which, while seemingly holding corersponding stratigraphic positions, 

 differ appreciably in faunal and lithological respects. In the case of the 

 Ordovician formations in the southern Appalachian Valley, at least, none 

 of the five formations with decidedly Atlantic faunas (Lenoir, Holston, 

 Athens, Tellico, and Ottosee) can be positively shown to have been laid 

 down at the same time when basins immediately to the west were occu- 

 pied by Gulf of Mexico waters. On the other hand, four of them, the 

 Ottosee shale, the Tellico sandstone, the Athens shale, and the Holston 

 marble, certainly date from times when the basins of the Ohioan province 

 were in a state of emergence. (See discussion of principle 17, page 554.) 

 Regarding the remaining Lenoir limestone, it is only because decisive 

 data are not yet at hand that it is provisionally correlated with the most 

 likely formation in the long standardized section of the Ohioan province. 

 In doing so we tacitly assume the existence of a land barrier between 

 their respective seas. Though the boundaries of the Paleozoic Appa- 

 lachian troughs always were potential barriers, it yet appears that their 

 functions were called into play less commonly to separate two neighbor- 

 ing contemporaneous seas than to form low ridges on and frequently 

 along the shore of larger land masses in which they were then included. 



(7) Interfingering overlaps in areas alternately submerged by waters 

 invading from different oceanic basins are of the highest importance in 

 disproving suggested contemporaneity of formations that seem to hold 

 like positions in the stratigraphic column. This principle is illustrated 

 on a broad scale by the interlapping edges of southern Atlantic and 

 Arctic Ordovician and Silurian formations in eastern Missouri, Ken- 

 tucky, and middle Tennessee. (See pages 367, 422, and figure 8, page 

 407.) Similar illustrations are seen on the north and south flanks .of the 

 interior domes, which, on account of differential oscillations, have been 

 tilted sometimes toward the east, at other times toward the west. (See 

 pages 415 to 419.) The latter examples are on a smaller scale than the 

 first, but, like them, are relatively simple. More intricate examples are 

 found in the Appalachian Valley. 



(8) That diastrophic movements resulting in long emergencies have 

 occurred between two lithologically similar, adjoining, and apparently 

 conformable stratigraphic units may often be established by the dis- 

 covery of intercalated formations. Examples are given in discussing the 

 lithological aspects of this principle on pages 526 to 532. 



