BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA 

 Vol. 18, pp. 1-28 April 5, i907 



CONCENTEATIOIsT AS A GEOLOGICAL PRINCIPLE 



PRESIDENTIAL ADDRESS BY ISRAEL C. RUSSELL * 



(Bead hefore the Society December 27, 1906) 



CONTENTS 



Page 



Introduction 



Statement of the problem ^ 



Analysis of the processes of geological concentration 3 



Primary divisions * 



Mechanical concentration 



Effects of gravity ^ 



Air and water currents ^ 



Ice currents ° 



Filtration 



8 



Sedimentation 1^ 



Mechanical concentration of liquids and gases 11 



Selective power of gravitation 11 



Sphere of influence • 12 



Chemical concentration 12 



The agencies involved 12 



Solution 12 



Residual concentrates 13 



Surface and subsurface precipitates 15 



Evapoi-ation 15 



Sublimation 19 



Chemical reaction resulting in precipitation 20 



Physical-chemical concentration 22 



Vital concentration ■ 25 



The agencies involved 25 



Carbon 25 



Calcium carbonate 26 



Silica 2T 



Summary 27 



In conclusion 28 



Introduction 



It is a matter of current knowledge among geologists that various 

 m.ineral substances of a greater or less degree of purity are at the present 



* Owing to the death of Pi-esident RusseU, this i^aper was read by Acting President 

 Davis. 



Manuscript received by the Secretary of the Society December 28, 1906. 



I — Bull. Geol. Soc. Am., Vol. 18, 1906 (1) 



