84 ANNALS NEW YORK ACADEMY OF SCIENCES 



the area, which would naturally occur chiefly along the borders of foreign 

 inclusions and conceivably in places where these inclusions had been 

 absorbed. In the case of the mines, it is also possible that the schistose 

 rock is an altered inclusion of the schist itself; but the entire absence of 

 quartz and muscovite and the presence at times of such minerals as 

 hypersthene tend to refute this view. Finally, it is possible that these 

 rocks may be inclusions of Highland gneiss ; but if they were, their action 

 on the igneous rocks would be undoubtedly similar to that of the schist, 

 and, moreover, their associations indicate that they are not foreign masses. 



This completes what the writer has to say concerning the origin of the 

 emery. From the points brought out, it is evident that the ore has in 

 most cases at least been formed by the action of the igneous rock upon 

 included material, thus giving rise to a magma supersaturated with re- 

 spect to iron and alumina; and out of this the corundum and its asso- 

 ciates crystallized according to the laws formulated by Morozewicz. The 

 evidence, while sufficient to justify a fairly positive statement, is, of 

 course, not entirely satisfactory, and the process is not as simple as indi- 

 cated. There seem to be no definite objections to this theory, however, 

 while those which confront that of magmatic segregation either through 

 the mass or at the cooler borders, appear to be insuperable. It might 

 also be suggested that the highly aluminous Hudson Eiver slates, which 

 probably once covered the district, furnished the alumina, but no trace 

 of them has been found in the field. There are inclusions of schist in 

 the diorite area which are generally associated with a fine black pyrox- 

 enite, but around which no emery has been found to the writer's knowl- 

 edge; although the farmers, judging from its toughness and color, be- 

 lieve that it is "full of emery." If it does not contain emery in any 

 place — except possibly the very narrow zone almost on the contact, which 

 we would expect by analogy from the effects at Crugers — it merely in- 

 dicates that these inclusions were particularly quartzose and compact and 

 retained their identity to an exceptional degree. As implied above, it is 

 not the large, well defined inclusions from which we would expect emery 

 to be derived, but rather the smaller fragments torn from these inclu- 

 sions and probably entirely absorbed. 



From this fact, it is evident that little can be predicted concerning 

 the probable extension of the emery. While pyroxenite, being low in 

 A1 2 3 and high in MgO, may readily attack the schist, the usual associa- 

 tion of the ore with this rock is not an essential limitation ; and its rela- 

 tions to the borders of the area are vague and irregular. Possibly, a 

 study of the mica schist at the borders nearest the mines might throw 

 light on the particular variety of schist most susceptible of absorption, 

 but this question has not been investigated by the writer. 



