604 E. O. ULRICH REVISION OF THE PALEOZOIC SYSTEMS 



moreover, resembles submergences of the preceding period more than 

 those next succeeding. This was explained on the supposition that fol- 

 lowing the continental emergence, Avhich prevailed for a longer or shorter 

 time between each of the successive periods, continental creep caused 

 general and relatively even lowering of the median parts of the continent. 

 Occasionally, this median subsidence proceeds to the stage of submer- 

 gence, resulting in a distribution of deposits that recalls preceding ages in 

 extent and areas covered. The idea is illustrated by the early Canadian 

 Stonehenge limestone in Pennsylvania and the Tribes Hill limestone in 

 New York, a zone that so far as it has been recognized agrees better with 

 preceding Ozarkian stages than does any succeeding Canadian submer- 

 gence. Surface warping and consequent changes in provincial boun- 

 daries, that is, in the form and oceanic connections of continental seas, 

 was delayed in this period to the next stage. 



Ordovician deposition preceding the period of abundant warping 

 evidently continued through even a longer time. This time is divisible 

 into two stages distinguished by wide differences in sea distribution, but 

 similar in that both indicate gradual submergence. In the first or Saint 

 Peter stage, the submergence was confined to the Mississippi Valley -and 

 areas adjacent thereto. Following the first, but preceding the second or 

 Stones Elver stage, suboceanic spreading caused reemergence of the 

 Mississippi Valley and gradually increasing submergence of the Appa- 

 lachian, Champlain, and Allegheny troughs on the east and the Arbuckle 

 region in Oklahoma on the south. Continental creep again becoming 

 effective, resulted in rather gradual northward overlap of Stones River 

 deposits. Consequently, while lower, middle, and upper Stones River 

 beds, aggregating between 1,000 and over 1,200 feet of limestone, are 

 found in certain parts of the Appalachian Valley, only late Stones River 

 deposits extend into the upper Mississippi Valley and into central New 

 York and southern Ontario. 



That warping occurred during the Stones River is clearly indicated 

 by faunal and stratigraphic studies in the Appalachian tract. These 

 show that Atlantic waters occupied the Champlain Valley during the 

 Crown Point age and also the eastern troughs of the valley in Tennessee, 

 where the Lenoir limestone was laid down. At about the same time 

 Gulf of Mexico waters filled troughs to the west of the Lenoir Bay, and 

 farther north, in the Marjdand basin, possibly mingled with Atlantic 

 waters (see table, page 54-1). Similar movements took place also fol- 

 lowing the Lenoir and preceding the Pamelia or upper Stones River 

 age, but, on the whole, the displacements of the strandline during the 



