■ OSCILLATOKY CHARACTER OF COATIJSENTAL SEAS 333 



ern trough, it apparently wedges out not far north of Lexington, Vir- 

 ginia. The Saratogan part of the Knox being rather generally absent in 

 the eastern fourth of the valley of east Tennessee, the series doubtless 

 overlapped also in that direction, but the fact is not readily demonstrable 

 in the field because the thin edge of the formation is covered by overthrust 

 faulting. Finally, clear evidence of Saratogan overlapping has been ol)- 

 served in the upper Mississippi Valley, but details remain to be worked 

 out. The advance of the Saratogan sea, though locally reversed at times 

 by warping of the continental surface, seems on the whole to have been 

 nearly continuous. The first notable interruption occurred at the close 

 of the Little Falls dolomite deposition in New York. This was -followed 

 by considerable warping and extensive sea withdrawal, so that the suc- 

 ceeding late Ozarkian geographic pattern is strikingly different from the 

 preceding Saratogan phases. So far as known, New York and Canada 

 and, excepting perhaps southwestern Virginia, the whole Appalachian 

 Valley remained above sealevel during the later Ozarkian submergence, 

 which seems to have been confined almost entirely to the interior areas of 

 the United States. It left considerable deposits in Missouri and Arkansas 

 (chiefly the Jefferson City dolomite) and possibly extended northward in 

 the Mississippi Valley to Minnesota and Wisconsin. The evidence of the 

 latter, however, is not entirely satisfactory. (For other Ozarkian over- 

 laps see pages 547 to 549.) 



The Ozarkian was followed by another great withdrawal of the sea. 

 Even where the succeeding Canadian limestones attain a thickness of over 

 4,200 feet, as in central Pennsylvania (see the Belief onte section in Part 

 III), the contact with the underlying Ozarkian rocks presents unmis- 

 takable evidence of an emergence gap. Also in southeastern Missouri 

 and northern Arkansas, where early Canadian deposits rest on a warped 

 and eroded surface of upper Ozarkian, the contact between the two is 

 unconformable and exhibits such undeniable evidence of inteiTening sub- 

 aerial conditions as old sinkholes and superficially decomposed and STil)se- 

 quently recemented cherty dolomite. 



Less widely recognizable, though not unimportant, breaks in sedimenta- 

 tion occur in the Canadian, but the next great emergence marks the 

 boundary between this new system and the revised Ordovician. And so 

 it goes on to the end of the chapter. Instead of very long enduring, con- 

 tinuously progressive overlaps, geologic history, as I see it, indicates fre- 

 quent interruptions and reversals of the tendency of the sea to submerge 

 the lands. 



