SIXTH REPORT OF THE DIRECTOR 1 909 1 35 



however, in areas containing Ozarkic and Canadian deposits the 

 boundary between the Cambric and the Ordovicic has been left 

 undecided, or it was drawn arbitrarily in the midst of what was 

 thought to be a great, sparsely fossiliferous, transitional series of 

 dolomites and limestones because its basal part contained surviv- 

 ing remnants of the Cambric fauna, and its uppermost ledges beld 

 fossils too much like Ordovicic species to be interpreted otherwise 

 than as Postcambric. 



This inharmonious practice was perhaps excusable under the pre- 

 vailing state of knowledge concerning Eopaleozoic history. So^ long 

 as the oscillatory character of the continental seas of this era and 

 the consequent variable localization of their deposits were not ap- 

 preciated, the formations occupying apparently similar stratigraphic 

 positions had to be correlated, and the observed differences in 

 their respective lithologic and faunal aspects were of course only 

 geographic changes or merely local phases. There was also con- 

 siderable excuse for individual difference of opinion as to which 

 of the organic and physical criteria were the most deserving of 

 confidence. 



But now, since it has been learned (i) that the Presaratogan 

 deposits in the Appalachian and Cordilleran troughs attain more 

 than sufficient thickness, and that their diastrophic history in 

 America fully satisfies the requirements of an ideal geologic 

 system;^ (2) that the great deposits of dolomite, limestone and 

 sandstone which usually succeed the Cambric were not laid down 

 in a continuous broad continental sea, hence that the magnesian 

 limestones at one place may be altogether younger or older than 

 those at another; (3) that these dolomites, limestones and sand- 

 stones are divisible or may be grouped into two distinct series, 

 largely independent in geographic distribution and each character- 

 ized by its own physical and faunal development; (4) that each of 

 these two series attains an aggregate thickness of over 4000 feet 

 of calcareous deposits, hence, that each is comparable in time value 

 to most of the systems now recognized; (5) that their independence, 

 first suggested by diastrophic and faunal evidence, is now firmly 

 established by the actual superposition of 4200 feet of Canadian 

 dolomite and limestone in central Pennsylvania on fully 2000 feet 

 of Ozarkic deposits; (6) that in the Appalachian region the whole 



' On questionable grounds, discussed elsewhere by one of the present 

 authors, Schuchert [Geol. Soc. Am. Bui. 20:513-22, 600-2] divides the 

 same interval into two systems (Georgia and Acadic). 



