The Phosphates of America. 67 



suggests that at the close of the cenozoic period the waters of 

 the ocean were probably more phosphatic than they are now. 



In these shallow warm seas there lived myriads of shell-fish, 

 many secreting phosphate as well as carbonate of lime, as is shown 

 by the analysis of a shell of lingula ovalis quoted by Dana as con- 

 taining 85.79 per cent, of phosphate of lime. Although no doubt 

 much of this phosphate was acquired by accretion at a subsequent 

 period, the fish-shells of these geological epochs were undoubtedly 

 more phosphatic than those of the present era. Fishes of all 

 kinds teemed in these waters, died, and their bones, while mostly 

 disappearing, served to increase the amount of phosphate of lime 

 in the limestone. 



Gradually the shores emerged from the seas, and even while 

 they rose came the great geologic era of semi-recent geology the 

 glacial epoch. 



The cold of this epoch, as we know, drove all and every living 

 creature which could travel southward, always southward. The 

 strongest survived the longest. Some sought the swamps and warm 

 estuaries of the Carolinas, but numbers were pushed to the south- 

 ern limit, and the great mammal horde of the tertiary epoch flocked 

 to the swamps and estuaries of Florida. There they died some 

 from want of food, some killed by the strongest, some drowned, 

 some of natural death, but most from the terrible cold wave. The 

 bones of these animals lay there in myriads ; some were preserved, 

 some rotted. 



At this time also the shallow sea was swarming with sharks, 

 manatee, whales and other denizens of tropic waters, many of them 

 also driven south by the change in the temperature in the northern 

 latitudes ; and their bones and teeth added to the " Valley of 

 Bones" which we now find along this southern shore. 



Then came the swing of the thermometric pendulum, and the 

 Champlain period was an era of melting of glaciers and of ice, 

 when most American rivers were fifty times the size they are to- 

 day, and after that, man first left records of his sojourn here. 



The Champlain floods were not so severe in their action in the 

 South as in the North, but no doubt it was during this period 

 that the Peace River pebble-formation and the soft-rock phos- 

 phates were largely deposited. 



While these quaternary changes were taking place, Florida was 

 still slowly but surely rising, and denudation began. Then once 

 more the slightly elevated peninsula gradually sank under sea- 



