Story of the Mississippi-Missouri. — Glaypole. 373 
monument of its existence in those wonderful bone-fields in 
the " bad lands " and other places from which palaeontologists 
are now extracting material for filling our museums and for 
reconstructing the mammalian history of the American Ter- 
tiary era. 
The longest of the new streams born on the eastern slopes of 
the western mountains was the Missouri. From its source it 
now flows at first eastward and then southward gathering on 
its right bank all the others that descend from the same 
range, the Yellowstone, the White, the Niobrara, the Platte 
the Loup and the Kansas, -and many of smaller size. Its 
rapid fall and headlong, impetuous course are to the geologist 
clear indications of a young river that has not yet worn down 
its channel. The sand and clay that are constantly borne 
down by its waters confirm the indication and fully bear out 
the belief that the Missouri river is still in the days of its 
youth. As we have seen, it only dates back to the middle or 
perhaps even to the latter part of the Tertiary era. 
The same changes that called the Missouri into being also 
contributed to increase the Mississippi. The elevation of the 
southern land and the increased mass of sediment brought 
down by the united waters carried the mouth farther and 
farther out to sea adding acre after acre to the great delta until 
now it extends more than five hundred miles to the south from 
the original mouth of the river near St. Louis. It is probable 
that nearly all this vast mass has been brought from the 
mountain region since the Missouri began to flow. The chief 
work of this river therefore has been to undo to a certain 
extent the elevation which produc5ed the Rocky mountains and 
the dry land of the west as far as the Pacific watershed. 
By this immense extension of its length its volume Avas pro- 
portionately enlarged. The creation of the great delta inter- 
cepted the other streams coming from the mountains further 
south and rendered them tributary to the Mississippi. The 
St. Francis, the White, the Arkansas, the Washita and the Red 
rivers are all in this condition. They have lost their individ- 
uality and instead of reaching the sea on the west of the great 
southern gulf they joined with the trunk stream and are lost in 
it before they enter the gulf of Mexico. Each of them con- 
tributed huge masses of material to the delta which therefore 
increases rapidly. Each no doubt had its own separate and 
