DESCRIPTIONS OF THE FORMATIONS. 47 



and covered with grass, growing on a deep, rich, comminuted soil of unsurpassed 

 fertility, and with scarcely any exposures of the underlying rock. 



The Bluff formation along the Missouri and Mississippi rivers is a very 

 peculiar and interesting one, resting upon and later than the drift. It is of a 

 slightly yellowish ash-color, very fine, not sandy, and yet not adhesive. It makes 

 an excellent soil, is easily excavated by the spade alone, and yet it remains so 

 unchanged by the atmosphere and frost, that wells dug in it require to be walled only 

 to a point above the water-line, while the remainder stands so securely without 

 support that the spade-marks remain upon it for many years. Road embankments 

 and excavations upon the sides of roads stand like a wall. The peculiar outline 

 of the bluffs along the Missouri river valley is very interesting. They are often 

 naked, entirely destitute of trees, and tower up from the river bottom-land, some- 

 times more than two hundred feet in height, and so steep, in some places, that a 

 man cannot climb them, yet they are not supported by a framework of rocks, 

 as other bluffs are, and not a rock or pebble of any size exists in them, except a 

 few calcareous concretions where lime-water percolates through them. It is a 

 lacustrine deposit, a shallow lake having, after the time of the Glacial epoch, 

 occupied the whole of the basin of the Mississippi before the great rivers had 

 cut their valleys down to their present depths. White. In Louisiana the Bluff 

 deposit contains three distinct groups of strata, the Port Hudson below, the 

 Loess next and the yellow loam above, over this is the alluvium, and below them 

 all, the drift. F. V. Hopkins. 



Earthy material brought together by the ordinary action of water is said to be 

 alluvia], and the soil or land so formed is called alluvium or alluvion. Diluvium 

 implies the extraordinary action of water. When the drift material covers the 

 surface, of course it forms the soil, but in drif tless regions the soil is an admixture 

 of clay, sand, lime, etc., derived from the disintegration of the rocks beneath, 

 with decomposed animal and vegetable substances. Where neither glacial nor 

 alluvial action has taken place as in some parts of our Southern States the 

 rocks as described by Dr. T. S. Hunt, are converted into a deep and strong soil, 

 having undergone a process of decay which has rendered them so soft, sometimes 

 to a depth of twenty feet or more, that they may be readily cut by a spade, 

 although retaining all the veins and layers which mark their original stratification. 

 Without having been broken or ground up, even the hardest rocks have quietly 

 mouldered into a soft, clayey mass, which, from its peculiar structure, has a 

 natural drainage and possesses, moreover, great fertility. 



The most important of geological formations is the last of all, the soiL On 

 this thin, superficial, earthy covering of our planet, depends the growth of all 

 vegetation, and on that depends all terrestrial animal life. But whether the 

 material forming the soil remains unmoved in the same spot where it was once a 

 solid rock, or is transported bodily by a glacier, or carried from the hills into the 

 valleys by running water, and moved from place to place by larger streams and 

 rivers, it was originally derived from the rock formations, therefore the agricul- 

 tural as well as the mineral resources of the country depends on its geology. 



This completes, in brief, the description of all that can be seen of the earth, 

 classified in geological order, from the oldest of the rocks, up to the sands which 

 are now daily washed to our feet, by the currents of the rivers and the waves of 

 the sea. 



