550 E. O. ULRICH REVISION OF THE PALEOZOIC SYSTEMS 



continent. Furthermore, since the intercalated formations are progres- 

 sive overlaps and there is little or no reason to believe that the top of 

 the underlying Cambrian formation — represented by the Conasauga in 

 the south and the Nolichucky and Honaker formations in Tennessee and 

 Virginia in the north — varies greatly in age, it follows that pre-Knox 

 erosion had little to do with the noted differences between the sections 

 at Knoxville, Tennessee, and Montevallo, Alabama. If anything, the 

 top of the Nolichucky in places is younger than any observed surface of 

 Conasauga. Aside from this, the stratigraphic hiatus is much greater in 

 Tennessee and farther north in the valley than in the vicinity of Monte- 

 vallo. 



The essential features of the foregoing example are duplicated in all 

 the systems that are well developed in the Appalachian Valley or in 

 adjacent parts of the Allegheny basin. They are similarly well displayed 

 by the Cambrian, the Canadian, the Ordovician, the Devonian, the Ten- 

 nessean, and the Pennsylvanian, all of which, save the Cambrian and 

 most probably also the Ordovician, have older beds at their respective 

 bases than are known elsewhere in American continental basins. It is to 

 be admitted, however, that on account of oscillation and shifting of seas, 

 the data necessary to a complete demonstration of the proposition in 

 these other cases are usually not found in the same area, correlation by 

 fossils and lithologic criteria and by stratigraphic overlap being required 

 to establish the sequence. The Silurian fails because it is less completely 

 developed in the valley than the others. The same may be said of the 

 Waverlyan. 



Complete emergence at close of Pamelia Stones Elver. — The principle 

 of complete emergence applies in a similar manner to many of the dias- 

 trophically separated formations; obviously, then, to the groups and 

 series also. As an example, we may take the Pamelia-Lowville break — 

 the latter formation a middle Ordovician datum plane often referred to 

 in this work. The time value of this break is more fully discussed under 

 the next principle. 



Wherever known, the Lowville is terminated below by a sharp break. 

 Where the formation rests on some bed of the lithologically similar Stones 

 Eiver formation, as happens very commonly, this break is seldom con- 

 spicuous, hpwever sharp it may prove to be on close investigation. But 

 when the Lowville rests on the upper Chazy or its equivalent, as at Chazy, 

 New York, and at Mercer sburg, Pennsylvania, or on either the Holston 

 or the Ottosee, as we find it in Hancock county, Tennessee, the contact 

 is not only sharp, but also conspicuous and clearly indicative of inter- 



