Natural History of La Salle County 



PART 11. 



THK GKOLOGY OF LA SALLE COUNTY. 



Geology has for its object a description of the 

 structure of our earth, of the character and arrange- 

 ment of the materials of which it is composed and the 

 explanation of the phenomena observed. This em- 

 braces a description of the rocks forming its outside or 

 surface, of the fossil remains of plants and animals 

 which they contain, such as bones, shells, teeth, stems, 

 leaves, etc. 



We must also observe the order in which the dif- 

 ferent beds occur, how they differ from each other, and 

 the fossils characteristic of each. And as far as possi- 

 ble we must account for the formation and present 

 condition of each stratum. We must also observe 

 what minerals and ores characterize each, the mode of 

 their occurrence, and, if possible, discover their origin. 



The field of geology is, therefore, a vast one. and 

 many of its problems are of a most perplexing nature. 

 But we may feel sure that the law^s of nature have 

 ahvays been the same, that a given cause has always 

 produced the same effect, ana that the causes which 

 today are producing certain results, produced the simi- 

 lar results which we find registered in the rock-sculp- 

 tured annals of past eternity. 



