614 E. O. ULRICH REVISION OF THE PALEOZOIC SYSTEMS 



satisfactory upper Cambrian^ an upper Cambrian that is definitely dis- 

 tinguished from the middle Cambrian by crustal movements whose effect 

 in displacing the Cambrian strandline is recognizable everywhere in N'orth 

 America to the east, and probably also to the west, of the Eocky Moun- 

 tains. In short, this proposed boundary between the middle and upper 

 Cambrian gives us a definite diastrophic line in place of the variously 

 or indefinitely drawn line of the past. But the upper Cambrian or Saint 

 Croixan of this work is in nowise the same as, nor is any part of it of the 

 age of, the typical New York Saratogan. 



Relations of the Cambrian to the Ozarhian.^^ — So long as the Eopaleo- 

 zoic was divided in but two systems, the only proper boundary between 

 them should have been the one here used in separating the Ozarkian from 

 the Canadian. But no two stratigraphers who had studied the problem 

 and were independent enough to form an opinion of their own seemed 

 able to recognize the boundary at the same position in the column and 

 to draw it consistently from place to place. Several matters were respon- 

 sible for this uncertainty. In the first place, the stratigraphy and inter- 

 relations of the deposits which are younger than the N'olichucky in the 

 Appalachian Valley, the Elvins formation in Missouri, and the Saint 

 Croix series in Minnesota, Iowa, and Wisconsin, and older than the base 

 of the Saint Peter sandstone series was quite misunderstood. Moreover, 

 the aggregate volume of the intervening beds was greatly underestimated, 

 and their faunal history almost unknown. A few trilobites and brachio- 

 pods were found in the Knox dolomite in Tennessee and in the Saratogan 

 series in New York, and as these belonged mostly to well known, though 

 Tather broadly conceived, Cambrian genera the beds containing them 

 were placed in that system. When well developed gastropods and cephalo- 

 pods were found, then the outcrop was stated to be of the upper part of 

 the Knox, which, being recognized as '"^Calciferous," made them post- 

 Cambrian. Had it been known that the "Cambrian" trilobites and the 

 ^^Ordovician" moUusks are interbedded in the Ozarkian section in Mis- 

 souri and the Appalachian Valley, a truer conception of the facts would 

 long ago have been attained. 



In the course of several seasons devoted to field studies in southern 

 Missouri a large and varied fauna has been collected from the strati- 

 graphic interval overlying the unquestioned Cambrian and underlying 

 the base of the Saint Peter sandstone. Excepting a few species described 



*2 The organic and physical principles chiefly involved in the division of the Eopaleo- 

 zoic into four systems instead of two are discussed in a recent paper by I^lrich and 

 Cushing on the age relations of the Little Falls dolomite, published in New York State 

 Museum Bull. 140. 1909, pp. 130-136. 



