STRATIGRAPHIC TAXONOMY 627 



which a rhythmically related suite of diastrophic events and consequent 

 sea shiftings occurred. 



The inadequacy of the evidence adduced by Schuchert in making two 

 distinct systems of the "Georgic" and the "Acadic," and especially the 

 inconsistency of his practice, will be best shown by comparing this case 

 with an almost identical later case in which at least equally clear evidence 

 was ignored. I refer, namely, to the relations of the Chazyan, particu- 

 larly the late Chazyan Blount group, of the Ordovician in the Appa- 

 lachian Valley to the .succeeding Mohawkian series. For the purpose 

 of this comparison the Blount group, which comprises the Normanskill 

 graptolite zone and other formations with Atlantic faunas, may be said 

 to correspond closely in geographic distribution and distinctness of faunas 

 with the lower Cambrian, while the succeeding Mohawkian may be com- 

 pared with the middle Cambrian. If anything, the distinctions which 

 Schuchert conceives to be of systemic importance in the older case are 

 even more conspicuous in the younger instance. And similar movements, 

 though in reversed order, occurred at the close of the Stones Eiver. But 

 who would think of dividing the Ordovician into a Stones Eiver system, 

 a Blount system, and a Mohawkian system? It is true Schuchert sepa- 

 rates the post-Mohawkian part of the Ordovician and places it, together 

 with the Eichmondian, into a '^Cincinnatic system," but this involves 

 somewhat different considerations that will be discussed in their proper 

 place. 



OZARKTAN PERIOD OR SYSTEM 



Definition of the term. — Under the term Ozarkian system I include 

 all the formations in the Appalachian Valley that can be shown to 

 be younger than (1) the top of the upper Cambrian Nolichucky shale 

 in northeastern Tennessee and (2) the top of the Conasauga shale in 

 southeastern Tennessee, northwestern Georgia, and northeastern Ala- 

 bama and which are older than the base of the Stonehenge limestone of 

 the Canadian system in southern and central Pennsylvania. Wherever 

 I have seen the contact with the underlying upper Cambrian shale or 

 shaly limestone evidence of interrupted sedimentation was noted. This is 

 true even in those cases in which gradual transition is suggested either 

 by increasing development of limestone upward in the Nolichucky or by 

 interbedding of thin layers of shale with relatively pure and more highly 

 magnesian limestone in the basal part of the Knox. Something of both 

 conditions was observed in the vicinity of Morristown, Tennessee, and 

 the latter condition is seen in Chestnut Eidge south of Sneedville. At 

 other places the boundary is sharp and clear, with shale beneath and 



