ROGERS, GEOLOGY OF THE CORTLANDT SERIES 77 



3. The ore is immediately associated with abnormal rocks, containing 

 sillimanite, cordierite, garnet, quartz or allanite, which are found no- 

 where else in the area, except around certain schist inclusions near 

 Crugers; or more rarely, it adjoins rocks which are normal except for 

 the spinel scattered through them. There is often a great abundance of 

 biotite around the ore, which is also characteristic of these inclusions. 



4. These rocks often exhibit evidences of shearing, faulting and crack- 

 ing, which is rare in other parts of the district, except around schist 

 inclusions. 



ORIGIN 



In reviewing the possible modes of origin of the emery in the Cort- 

 landt Series, it appears evident that only two are plausible: the emery 

 may be pyrogenic, due to magmatic segregation, or due to the absorption 

 of some of the numerous schist inclusions in the area. The evidence 

 may perhaps be more effectively weighed if we first briefly consider the 

 artificial production of corundum and its occurrence in other districts. 



Artificial Production of Corundum 



Several French geologists have been especially active in the field of 

 synthetic mineralogy, 61 but their results in this connection are of little 

 importance. Many of them worked with alumina and artificial salts, 

 so that their processes find no equivalent in nature; others dissolved 

 alumina in various melted minerals, adding in some cases a trace of 

 ammonium fluoride or some similar salt. These last experiments are of 

 more importance in a geological way, but they appear to have no appli- 

 cation to the Cortlandt Series. 



The only relevant case that the writer has been able to find of the 

 production of corundum by the simple fusion of a mineral is described 

 by Vernadsky. 62 He observed the formation of corundum and silli- 

 manite in a melt of muscovite, in the course of his experiments on the 

 genesis of sillimanite. 63 



Probably the most important investigation from a geological point of 

 view is that undertaken by J. Morozewicz. 64 Basing his work on the 



61 FouQufi and Levy. Synthese des Mineraux et des Roches, Paris. 1882. See also 

 L. Bourgeois, "Reproduction artificielle des mineraux." in Fremy's Encyclopedic 

 chimique, II, pt. 3, p. 63. 



82 On the Sillimanite Group, and the Role of Alumina in Silicates. Moscow, p. 83. 

 1891. (Russian.) He also describes the formation of sillimanite from clay in "Sur la 

 reproduction de la Sillimanite," Bull. Soc. franc de mineral., p. 256. 1890. 



63 Corundum is commercially manufactured by the Norton Emery Company at Niagara 

 Falls by the fusion of bauxite, previously rendered anhydrous by thorough heating. 



64 "Experiment. Untersuchungen iiber d. Bildung d. Mineralien im Magma." Tscher- 

 maKs mineral, und petrog. Mittheil., XVIII, pp. 1-90 and 105-240. 1898. 



