640 E. O. ULRICH REVISION OF THE PALEOZOIC SYSTEMS 



Principles based partly or ivliolly on inference — (9) Relation of area! 

 extent and thickness of formations to rate of submergence. — Great area I 

 extent of relatively thin formations in which progressive diminution by 

 overlap is very gradual indicates rapid submergence of broad, flat areas, 

 shallow seas and low lands, and is marked by extraordinary uniformity 

 of faunas. The best examples are among the Arctic and north Atlantic 

 invasions, of which the Decorah shale and the Prosser limestone extend 

 southwardly to or beyond Missouri. (See pages 367 to 371.) Even 

 more extraordinary than these is the late Richmond coral zone, which is 

 recognized in Russia, Baffinland, in Alaska and as far south in the Missis- 

 sippi Valley as Thebes, Illinois, and in the Cordilleran basin to New 

 Mexico and western Texas. (See page 306.) Of the numerous southern 

 invasions those that transgressed widely and rapidly are the Lowville, the 

 late Eden, the Brassfield, the Osgood-Rochester, and the Onondaga. 



Thick, geographically limited formations, especially those which con- 

 sist chiefly of land detritus, indicate relatively high relief of lands and 

 deposition confined to the continental shelf and to relatively deep and 

 narrow submarginal troughs. Such are most of the Paleozoic formations 

 exposed between the shore of the Atlantic and the Appalachian Valley, 

 and the similarly located formations on the western side of the continent. 



(10) Correlation by evidence of sea-filling and tidal flats. — Sun- 

 cracked and ripple-marked marine deposits, also intraformational con- 

 glomerates and worm-bored surfaces, found singly or together, indicate 

 either sea-filling and, consequently, shallowing of seas and impending 

 emergence, or the advance of a shallow sea over broad tidal flats. In 

 the former cases these phenomena occur in the closing stage of a period 

 of uninterrupted sedimentation; and the development of the individual 

 beds so marked is often decidedly local; for example, the local occur- 

 rence of sun-cracked and rippled surfaces in the upper part of the 

 Pamelia Stones River in the vicinity of Kingston, Ontario. A broader 

 example of shallowing preceding a long emergence is found in the very 

 widely distributed late upper Cambrian zone which is commonly marked 

 by thin beds of "edgewise" intraformational conglomerates. Although 

 this zone is very generally distributed, the individual beds of conglom- 

 erate are very limited in areal extent. In the alternative cases, wherein 

 the phenomena are produced under conditions of sea transgression over 

 tidal flats and beaches, the characteristically marked beds or surfaces 

 are, as a rule, much more extensive. Good examples are seen in the 

 lower and middle parts of the Lowville limestone in the Appalachian 



