STRAND-LINE DISPLACEMENTS 485 



as the maximum emergence succeeded the Shakopee dolomite this fixed 

 the name for the 



Shakopee emergence (see map, plate 53). — The area of this emergence 

 was of considerable extent and the waters were drawn away to the south. 

 According to the paleogeographic map, about 12 per cent of North Amer- 

 ica remained under the sea and about 26 per cent of the United States. 

 This emergence was seemingly not of long duration, for a secular move- 

 ment was again recorded in Acadia and Appalachia. The Green Mountain- 

 Chilhowee axis in the north and south became a definite barrier for the 

 separation of most subsequent Ordovicic waters. While this secular 

 change locally affected the seaways in Acadia and accentuated the syn- 

 clinal seas, yet it could not have been the cause for the next important 

 .alteration in the strand-line. The introduction of this positive movement 

 closed the Ozarkic period and began the 



Canadic period or system 119 — Beekmantown transgression (see map, 

 plate 54). — This invasion had the character of a transgressive sea, but was 

 not nearly so positive as that of the Saint Croix, being about that of the 

 Ozarkian. For the continent the figure was about 23 per cent, and for 

 the United States about 30 per cent. The Sonoran sea, with its Pacific 

 faunas, flowed around south Missouria and widely west of Appalachia. 

 •continuing with its characteristic life out through the north Saint Law- 

 rence trough, or more properly the Chazy trough, its blended faunas 

 •occurring in Newfoundland. Throughout it was a sea forming dolomite- 

 limestone, the deposits attaining a thickness of 2,500 feet in the Missis- 

 sippian sea. On the other side of the Green Mountain axis, however, in 

 the Levis trough, occur clastic rocks with different faunas, best compared 

 with those of Scotland and Sweden. These were derived from the Saint 

 Lawrence sea, which at this time appears to have had no connection with 

 the Chazy trough, being clearly of another faunal realm. As is shown 

 •elsewhere by Ulrich, the Beekmantown sea was oscillatory, and for a long 

 time the invasion was fairly persistent. Without definite cause, appar- 

 ently, the strand-line again became negative, and there resulted the 



Saint Peter emergence (see map, plate 55). — According to the map, 

 this emergence left but 12 per cent of the North American continent 

 submerged and 22 per cent of the United States. It is probable, how- 

 ever, that the waters were withdrawn even more than is represented by 

 these figures, for there is a hiatus in the deposits of nearly all the known 

 outcrops. The emergence appears to have been of short duration, and 

 "the faunas marking it are best known in Missouri and Arkansas. The 

 weathered sands of the Saint Croix deposits composed the regolith in the 



119 Lower Ordovician or Canadian of American stratigraphers. 



