138 UNIVERSITY OF MISSOURI BULLETIN 



filling of desert land basins are all effected by the action of 

 constructive processes. 



Until within the last quarter of a century geologists con- 

 cerned themselves almost exclusively with the study of this 

 phase of geological process. Occasional reference was made 

 to the other side even as far back as the time of Hutton, but 

 no study was made of its operation. The study of geological 

 processes was a study mainly of processes that had gone on 

 or were going on chiefly on the sea bottom. Geological his- 

 tory was to a great extent the history of those parts of the 

 earth's surface that had been under the sea at various times 

 and concerned them only while they were in this position. 



Constructive work cannot take place without its corre- 

 sponding destruction. Building cannot take place without 

 quarrying or without acquiring the material from some source. 

 The gradual building up of the continents by the slow deposi- 

 tion of sands, silts, clays, and pebbles during temporary sub- 

 mergence could not possibly take place without the destruc- 

 tion of land areas to furnish the material. Land material, 

 when once it reaches sea bottom, cannot return whence it 

 came except through the intervention of entirely different 

 forces and processes from those which brought it into that 

 position. The sea bottom is the zero point of earth surface 

 activity as death is the zero point of life activity of organic 

 beings. Material once reaching that position remains there 

 forever except through the intervention of some other pro- 

 cesses than those acting on the land surface. 



The processes acting on the surface of the land are the 

 destructive processes. Their existence has long been known 

 and referred to. In fact they are seen in operation by man 

 at all times, but the laws governing their operation had not 

 been studied, much less formulated, until very recent times. 

 The first general statement of their operation was made by 

 Major Powell in 1870. Since that time much work and 

 thought have been spent on their investigation. This has 



