CHAPTER II 



SURFACE DEPOSITS. 



The surface deposits, which it is proposed to discuss in this 

 chapter, are those to which the names of Drift, Bluff, and 

 Alluvium have been applied; all of which rest upon or above 

 the stratified rocks that form, so to speak, the foundation of 

 our State. It is from these almost alone that our soil has 

 been derived, and, covering the underlying rocks so generally, 

 the materials of which they are composed are more familiar 

 to our eyes than any others which enter into the composition 

 of the earth's crust. 



1. DRIFT. 



The deposit to which the name of Drift is applied, has a far 

 wider distribution than any other surface deposit. It meets 

 our eyes almost everywhere, covering the earth like a mantle 

 and hiding the stratified rocks from view, except where they 

 have been exposed by the removal of the drift through the 

 erosive action of water. It forms the soil and subsoil of the 

 greater part of the State, and in it alone many of our wells 

 are dug, and our forests take root. Occasionally it is itself 

 covered by another deposit; as for example, by the Bluff 

 Deposit of western Iowa, in which case, the latter forms the 

 soil and subsoil. No other deposit, however, intervenes 

 between the drift and the stratified rocks. 



Physical Composition. The drift is composed of clay, 

 sand, gravel, and boulders, promiscuously intermixed, without 

 stratification or any other regular arrangement of its mate- 

 rials. It varies in character in different parts of the State, 



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