Handbook of Paleontology 305 



by the hematite, and so the ore is termed "fossil" iron 

 ore. The name "pea" or "oolitic" iron ore is also ap- 

 plied to it because some beds are made up of rounded 

 grains of a concretionary nature. 



The lower beds of the Upper Silurian (the Salinan) 

 through ' the Appalachian region are missing south of 

 Virginia, the uppermost Silurian beds resting upon the 

 Middle Silurian (Niagaran) except, perhaps, in south- 

 western Virginia. No typically marine Salina de- 

 posits are known anywhere. The elevation of the land 

 and the withdrawal of the sea at the close of the 

 Niagaran rejuvenated the rivers of Appalachia, and 

 pebble and sand deposits were built up in the Appa- 

 lachian trough, the latter now forming typical red beds 

 through the alteration of the iron content. In cen- 

 tral and western New York, in northern Ohio, in 

 Michigan and parts of Ontario the Salina beds are 

 represented by shales and lime muds alternating with 

 salt and gypsum. In southern Michigan and adjoin- 

 ing areas the Salina formations are developed to their 

 greatest thickness. In New York an extension of the 

 red beds of the east underlies the salt beds, but dies 

 away westward (Vernon shale). As mentioned above, 

 the indications are that the Salina beds were accumu- 

 lated in shifting lagoons or shallow arms of the sea, 

 partially cut off from the sea by a barrier and sur- 

 rounded by a desert region due to an arid climate. In 

 time concentration of water in these lagoons became 

 so great that common salt and other salts were pre- 

 cipitated. In this way pure salt deposits could ac- 

 cumulate to considerable thickness, but at times they 

 would be overlain by muds brought into the lagoons 

 by desert streams swollen by heavy rains. The salt 



