PHYSICAL-CHEMICAL CONCENTEATION 25 



through the agency of highly heated percolating water seems to have 

 followed. In fact, it seems inadvisable at present to attempt to draw 

 a dividing line between the results of crystallization and segregation of 

 minerals directly from magmas and subsequent concentration, owing 

 to the action of percolating heated water while the mass was slowly 

 cooling. These two processes must grade one into the other and their 

 results merge in a complete manner. 



Magnetic segregation, during which the heavier minerals crystallizing 

 out of a magma migrate toward the bottom of the mass and lighter 

 minerals toward its summit, or outer portion, appears to be a funda- 

 mental principle which should lead to the production of definite concen- 

 tration. Examples of this method appear to be furnished at the Sud- 

 bury district, Canada, as described by Colman. 



Vital Concentration 

 the agencies involved 



In attempting to briefly review the various ways in which living 

 organisms lead to the concentration of mineral matter, two divisions 

 should be made — one to include what may be termed the geological 

 work of plants, and the other to embrace the similar functions performed 

 by animals. Under each of these divisions the composition of the sub- 

 stances segregated suggest subordinate headings. For the sake of econo- 

 mizing space, however, only certain typical examples will be cited. 



The principal substances of geological importance segregated by plants 

 and animals as a part of their vital functions are carbon, silica, and 

 calcium carbonate; but a more extended analysis would include potash, 

 soda, magnesia, sulphur, iodine, etcetera. 



CARBON 



In the whole range of selective functions, either inorganic or organic, 

 under review, perhaps no better illustration is furnished of the prin- 

 ciple made prominent in this address than by the manner in which land 

 plants decompose the carbon dioxide of the air and fix the carbon in 

 their tissues. This process of obtaining carbon from an invisible gaseous 

 source and giving it a solid form is the mainspring of a great series 

 of geological as well as of industrial results. The processes by which 

 peat beds and other accumulations of carbon are produced are too well 

 known to be discussed in detail at this time. An important auxiliary 

 principle of wide application, of necessity operating in conjunction with 

 the principle of concentration, however, is perhaps best illustrated by 



III — Bull. Geol. Soc. Am., Vol. 18, 1906 



