Z I. C. RUSSELL CONCENTRATION AS A GEOLOGICAL PRINCIPLE 



time being separated through the agency of natural processes from 

 other substances or gathered from a previously widely disseminated 

 state and placed by themselves. To this general process the term geo- 

 logical concentration has been applied. It is also well known from 

 the study of mineral veins, residual earths, etcetera, that similar processes 

 of concentration have been in operation throughout geological time, 

 and that in obedience to a law of nature, as yet inscutible, whereby like 

 seeks like, most mineral substances of commercial value have been segre- 

 gated in veins, beds, and other deposits, and thus become available for 

 human uses. ISTo systematic attempt seems to have been made, however, 

 to formulate the many and frequently highly complex processes by which 

 the concentration of mineral substances through the action of natural 

 agencies is brought about. It is with this phase of geological study that 

 the present address is concerned. 



Statement of the Problem 



During the flow of streams heavier is separated from lighter material 

 in suspension or rolled along the bottom, and gold, platinum, tin ore, 

 and other substances of high specific gravity are frequently retained 

 in depressions of the stream's' beds, while substances of less specific 

 gravity are carried on. Water emerging at the earth's surface as springs 

 contains calcium carbonate, silica, etcetera, in solution, which in many 

 instances are deposited as chemical precipitates. Plants select carbon 

 from the carbon dioxide of the air and secrete it in their tissues, thus 

 accumulating material suitable for the production of beds of peat and 

 coal. These and other similar or analogous processes whereby concen- 

 tration of mineral matter results are now in operation and should, as it 

 seems, to be duly recognized as constituting a distinct and important 

 chapter in dynamical geology. 



Under the uniformitarian doctrine that "the present is the key to 

 the past," it is evident that a study of the processes by which the concen- 

 tration of mineral matter is now being brought about should furnish 

 a means for determining the nature and mode of action of the processes 

 by which similar results were produced during past time. In other 

 words, a knowledge of the processes of concentration now in operation 

 furnishes a means for translating the records of former combinations 

 of agencies and conditions into terms which may be defined by observing 

 the results produced by similar combinations at the present day. In the 

 same manner that ripple-marks, shrinkage cracks, raindrop impressions, 

 etcetera, on ancient sandstones furnish evidence as to the geographical 



