PREFATOEY NOTE 



In the work here presented the writer has endeavored to 

 bring together in systematic form the results of several years' 

 study of the phenomena attendant upon rock degeneration 

 and soil formation. Although beginning with a discussion 

 of rocks and rock-forming minerals, the work must be con- 

 sidered in no sense a petrology as this word is commonly 

 used. "What is here given relative to the origin, structure, 

 and composition of rock masses is regarded as an essential 

 introduction to the chapters on rock-weathering. The por- 

 tion dealing with the structure and composition of the resultant 

 materials is an essential corollary to these same chapters. 



It is believed that no apology is necessary for bringing out the 

 present work. The origin, structure, and mineral composition of 

 rocks, particularly the eruptive varieties, are matters which have 

 of late received much attention. In fact, it is to these rocks that 

 the petrologists have devoted their best efforts. Since the intro- 

 duction of the microscope into petrographic work, there has, how- 

 ever, been very little time devoted to the study of rocks in a 

 weathered condition. The chemists have made analyses, but have 

 disregarded the physical and mineralogical nature of the material 

 analyzed. Other workers have studied the physical properties 

 of rocks decayed, — in the form of soils, — but have in their 

 turn disregarded their mineral and chemical nature. The 

 writer has aimed to bring together here such results obtained 

 by these workers in divers fields as it is believed will be for 

 the mutual benefit of all concerned. The state of comminu- 

 tion reached by rocks during the processes of long-continued, 

 secular decay, and the amount of leaching such have under- 

 gone, are certainly of as much practical interest to the agri- 

 culturist as of theoretical interest to the geologist. 



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