The Phosphates of America. 4.5 



CHAPTER IV. 



THE PHOSPHATE DEPOSITS OF SOUTH CAROLINA. 



THE amorphous and nodular deposits of phosphate of lime thus 

 far discovered in the United States have been found in that portion 

 of the rocks of the fourth geological period or " Cenozoic " time 

 known as the Tertiary Formation, or " age of mammals," which 

 immediately preceded the Quaternary formation, or "age of 

 man." 



It is probable that the earth's surface really began to assume its 

 present geographical aspect in this tertiary age, and a great part of 

 its fauna and flora either closely resembled or was identical with a 

 large number of our existing familiar species. Chief among its 

 characteristics was a marked and continuous subsidence of the 

 seas and an accompanying increased elevation of the land. The 

 seas underwent evaporation ; lagoons were formed ; marshes were 

 dried up; lakes were drained, and mountain chains arose and towered 

 above deep valleys. The climatic conditions were next revolution- 

 ized, for the even temperature communicated by the earth's interior 

 heat to an unbroken surface could no longer prevail. A redis- 

 tribution of fauna &&& flora hence necessarily ensued, and number- 

 less species were naturally exterminated before perfect acclimation 

 could be accomplished. The fossilized remains of these extinct 

 species, including incredibly gigantic reptiles and sea monsters, con- 

 tinue to afford a most interesting field for the study of paleontology, 

 and have enabled us to recognize the pachydermatous anoplothe- 

 rium as the oldest typical mammal, and to trace the succeeding 

 true ruminant and carnivora and the endless swarms of shell-fish 

 and bivalves right down to the present time. 



The subdivisions of the tertiary age embrace three eras, which 

 are respectively known to geologists as follows : 



The Eocene Era, or age of nearly extinct species. 



The Miocene Era, or age of which the species are more than 

 half extinct. 



The Pliocene Era, or age of which more than half the species 

 are still living. 



The rocks of the tertiary have been classified according to 



