STRAND-LINE DISPLACEMENTS 491 



Cayugan emergence (U. and S., 1902, 618) (plates 69-71). — Without 

 apparent cause, as far as the North American continent is concerned, an 

 emergence began with the Guelph. As usual, the withdrawal of the sea 

 was again fairly rapid. With the Guelph the great northern or Hudson 

 sea vanished, and possibly even earlier all the Indiana basin had disap- 

 peared. For a long time the known oceanic extensions were then confined 

 to the northeastern part of the United States in the northern Appa- 

 lachian, Ohio, and northern Indiana basins, and farther northeast in the 

 Saint Lawrence sea of the Acadian region. According to the maps, the 

 emergence is represented by the following figures : 



North America. United States. 



Guelph 31 per cent 20 per cent 



Lower Salina 6 " " 10 " " 



Bertie 5 " " 10 " " 



Lower Manlius 5 " " 10 " " 



In the United States, after the Guelph, these seas were very shallow — 

 not normal marine waters. The sedimentary record is one either of red 

 shales with salt and gypsum, or thin dolomites or water-limestones. The 

 seas were those of an arid climate, with salt pans and shallow stretches 

 alternately exposed to the effects of the sun, as demonstrated by the sun- 

 cracked "ribbon limestones" or calcareous shales to be seen in many widely 

 separated places. At last the greater part of these waters subsided, and 

 the Siluric ended with an emergence that was nearly as extensive as the 

 one at the beginning of this period. Suess also points out this emergence 

 by stating: "The Silurian concludes in England, as in North America, 

 with an unmistakable and considerable diminution in the depth of the 

 sea" (11:225). 



Devonic period or system — Onondaga transgression (Ulrich and Schu- 

 chert, 1902, 652. See maps, plates 72-76). — The widespread emergence 

 at the close of the Siluric continued into the Devonic, and for a time, which 

 may be measured by the Helderbergian and Oriskanian deposits, the sea 

 was oscillatory. This movement did not become decidedly positive until 

 toward the close of the Oriskanian. In the east the seas of this interval 

 appear to have been of the synclinal type, while those of the Mexico em- 

 bayment represented the early stages of the transgressive sea. Late in the 

 Oriskany the flood began to spread westward through New York, and very 

 early in Onondaga time the sea became general along the western side of 

 the Cincinnati axis. Through the Mexico embayment the warm waters of 

 the Gulf of Mexico spread, and reached even as far as James bay. This sea 

 brought in the well known coral fauna, best represented in the region of 

 Louisville, Kentucky. At the same time the northern Atlantic extended 



