80 ANNALS NEW YORK ACADEMY OF SCIENCES 



The Theory of Magmatic Segregation 



That magmatic segregation is possible is proved by the experiments of 

 Morozewicz, who has shown that corundum may separate out of a super- 

 saturated magma and that the associated minerals, which were formerly 

 supposed to be due in every case to contact action, may have a similar 

 origin. If it has so formed, we should expect it to show probably a close 

 association with the border of the igneous area, as in the case of the Caro- 

 lina peridotite, since such an abundance of early-crystallizing minerals 

 would be carried to the borders by convection currents, or by some process 

 akin to Soret's principle. It shows a rather close association, in some 

 cases occurring practically on the border, while the most important, mine 

 is located within a thousand feet of it. Other occurrences are, however, a 

 mile or more removed. The ore is disseminated to a certain degree 

 through the surrounding rocks, which are sometimes otherwise normal 

 and sometimes extraordinary aggregates of the minerals which have been 

 shown to be associated with pyrogenic corundum under certain conditions. 

 Moreover, the magnetite which is associated so plentifully with the ore is 

 known to be in other localities a basic segregation, 75 although in such cases 

 it is usually highly titaniferous. It is possible, therefore, that the ore 

 has separated out of the magma as an original pyrogenic constituent. 



There are certain phenomena, howeAer, which this hypothesis does not 

 account for. If the emery shows any preference for the borders, as in the 

 case of the Carolina peridotite, it should show a distinct preference, occur- 

 ring directly on the borders as a sharp contact but grading into the 

 igneous rock. In no case, however, was it observed directly on the border 

 or even on the margin of an inclusion. Moreover, in none of the cases of 

 pyrogenic corundum cited by either Morozewicz 76 or Lagorio 77 is magnet- 

 ite a very important constituent ; certainly in none does it occur in excess 

 of the corundum. Basic segregations of magnetite, furthermore, are 

 usually very titaniferous, 78 while in the Cortlandt Series, the average of 

 Ti0 2 in the four different emery analyses is 1.90 per cent, while in seven 

 analyses of the important igneous rocks of the district, the average is 2.15 

 per cent., running much the lowest in the pyroxenites. Nor does this 

 theory explain the dynamic action which is so evident at the mines and 

 almost confined to them ; nor the streaked appearance of the ore in a very 



75 See for a summary Kemp's Ore Deposits of the U. S.. p. 171, etc. 1906. 



78 Min. pet. Mitth., XVIII, 212-219. 1898. 



"Zeit. Kryst. Min., XXIV, 285. 1895. 



78 Thus, for example, the ore from the classic locality for this process. Taberg, is 

 almost an ilmenite ; similarly the Cumberlandite of Rhode Island, the titaniferous mag- 

 netites of the Adirondacks, etc. 



