302 New York State Museum 



and south of this. The Richmond covers a greater pro- 

 portion of the continent than any subsequent series of 

 Silurian deposits. At the close of the Lower Silurian 

 there was a great but not complete emergence followed 

 by another great but oscillating submergence, that of 

 the Middle Silurian (Niagaran) epoch. As in the pre- 

 ceding period (Ordovician) the highlands were along 

 the borders of the continent and the interior basin was 

 little above sea level. The Cincinnati dome was of no 

 significance as a topographic feature until after Lower 

 Silurian time when distinct marine basins were de- 

 veloped on both the east and west sides. The second 

 flooding of this interior low area was somewhat in- 

 ferior in aggregate extent to the one that took place 

 in Lower Silurian (Richmond) and at this time ap- 

 proximately 20 per cent of the continent was under 

 water. These floods were chiefly from the Arctic 

 ocean, but smaller seaways spread northward from the 

 Gulf of Mexico and in the west a seaway extended 

 from California through Idaho to Canada. Little is 

 known of the Cordilleran sea. Small seaways con- 

 nected with the North Atlantic in the St Lawrence 

 and Acadian areas, and there were times when there 

 was a connection between the St Lawrence waters 

 and the Appalachian trough. Epicontinental seas were 

 again restricted in the Upper Silurian. Salinan time 

 in northeastern North America is characterized by 

 shifting lagoons and an arid climate. Along the north- 

 ern part of the northeastern area of the interior sea 

 salt lagoons were separated off and in these was de- 

 posited a series of red marls and shales interstratified 

 with gypsum and rock salt. Following these came a 

 freshening of the Salina lagoons and the deposition of 



