u: r 



CHAPTER I. 



DRIFT DEPOSITS OF ILLINOIS. 



In the preceding volumes of my report on the Geological Sur- 

 vey of Illinois, no exhaustive discussion of the character and 

 extent of the superficial deposits of this State was attempted, 

 because the i. y data were not attainable from an exami- 



nation of the natural exposures of the formation alone. 



Subsequently, in the development of our coal resources, many 

 shafts were sunk through the superficial deposits in various por- 

 tions of the State, which, with other artificial excavations, have 

 afforded all the - y data for a more comprehensive treat- 



ment of the subject: and some of the most instructive sections 

 of the drift deposits obtained in this way we shall present in 

 detail in the following pa- 



These deposits consist mainly of clay, sand and gravel, which 

 oread uuconformably over the stratified rocks, covering 

 them to the depth of from ten to more than three hundred and 

 fifty feet. Over large aivus in the central portions of the State 

 they extend far below the drainage level of the streams, and 

 consequently only the upper portion of the deposit can be seen 

 in the bluffs and' banks of the water com- 



The drift deposits are important in an economical point of 

 view : Fhft Because they determine the character and produc- 

 tive capacity of the soil upon which all other industries are 

 !y dependent. Soils consist mainly of pulverized rock, to 

 which is added such organic substan result from the 



growth and decay of animal and vegetable organisms upon the 

 surface, and the soils of Illinois, being the result of disintegra- 

 tion of the limestones, sandstones, shales, etc., which constitute 

 the various paheozoic formations of the Mississippi valley, con- 

 tain all the essential mineral ingredients that are required to 

 constitute a soil of surpassing fertility. 



