second-largest zvading bird. It nests fron! Quebec to Florida 

 hut most of its numbers winter in the South. Center below: 

 Typical of the vast number of wading birds that live in the 

 delta or pass through it on migration are this gallinule, 

 coot, Louisiana Heron, and Snowy Egret. 



upper hand and burst out with a new tongue of land (Arc II on 

 map). This happened four times, but then the river encountered 

 some assistance, as it were, from the land in its persistent battle 

 with the sea, for it had pushed so far out that it had begun to 

 form a "hook" and thereby created a slight whirligig or counter- 

 current to its left side. This enabled it to make such headway 

 that it did virtually dam itself up (Arc V on the map) and, 

 having thus covered its left flank, it burst out at its old mouth 

 (Arc IV), where it is today, penetrating into "enemy territory." 

 A Louisiana survey has calculated that the Mississippi carries 

 one million tons of sediment to the sea every day of the year. In 

 a year, this is equivalent to a block of land one square mile in 

 area and three hundred feet high. During the eleven thousand 

 years since the last "retreat" of the ice up north, it has there- 

 fore dumped sediment to a depth of two hundred feet over the 

 entire eighteen thousand square miles of its delta: yet that delta 

 is still only just above sea level! Where has it gone? Down 

 below, to form a great inverted dome in the earth's crust, 

 creating thereby complex pressures and tensions that affect a 

 wide area around; for you cannot push a solid into another 

 solid without something giving way. It is a strange thing that 

 deltas, which appear to be the lowest and softest places on earth, 

 really form some of the hardest "nuts" in its crust. When a 

 whole subcontinent sinks, as northern Australia has done, among 

 the last things to go down are the deltas, as is seen in the Aru 

 Islands in the Arafura Sea. which are only the old delta of a 

 vast river that once ran north off that land. 



DOMES OF SALT AND SULPHUR 



The amount of sediment actually accumulated in the Mississippi 

 delta is not known, but geologists state that it is more than thirty 

 thousand feet in depth. At the present rate of deposit, this 

 represents six and a half million years, which takes us back to 

 about the beginning of the so-called Pliocene era, the stage 



