220 



University of California. 



[vol. :s. 



"corundum never occurs as an essential constituent of rocks, 

 with the exception of emery, which, together with iron oxides, 

 forms independent bodies in the crystalline schists. It appears 

 only as an accessory constituent in granites, gneisses, granular 

 limestones and dolomites, and is constantly accompanied by 

 spinel, rutile and sillimanite." 



In Rosenbusch's last book, "Elemente der Gesteinslehre," 

 1898, rocks of this interesting character are not recognized. 

 These facts are not mentioned by way of criticism of the text- 

 books, but simply to emphasize the recency and practical 

 simultaneity of the various discoveries referred to. These dis- 

 coveries have, moreover, been supplemented, and, indeed, in a 

 large measure anticipated, by the brilliant synthetic studies of 

 Morozewiez.* 



In contrast to the state of knowledge at the date of the text- 

 books above referred to we have to-day a considerable body of 

 information -on the occurrence and character of corundiferous 

 igneous rocks. In India Holland"!" has described a corundum 

 syenite. In Russia Morozewicz has described corundum syenite 

 and corundum pegmatite from the Uralst as well as a more basic 

 type consisting of anorthite and corundum together with some 

 biotite with accessory spinel, apatite and zircon, to which he 

 gives the name Kyschtymite. In Eastern Ontario, Canada, 

 there have been discovered areas of corundiferous syenites, 

 nepheline-syenites and anorthosites which are the most extensive 

 and important occurrences of corundiferous igneous rocks at 

 present known, whether they be regarded from a petrological 

 standpoint or as a source of supply for the best quality of 

 abrasive material. These rocks have been described by Professor 

 W. E. Miller§ and others. The occurrences of corundiferous 

 rocks in the United States has recently been reviewed by J. H. 

 Pratt. 1 1 The most noteworthy occurrences are those of Montana, 



* Experinientelle Untersuchungen iiber die Bildung der Minerale im Magma, 

 Tsohermak's M.u.P.M. N.F. Band XVIII, 1899. 



t Manual of the Geology of India, Economic Geology, Pt. 1, 1898. Memoirs, 

 Geological Survey of India, Vol. XXX, Pt. 3, 1901. 



J Op. cit. 



§ Rpt. Bureau of Mines, Vol. VIII, 2nd pt., 1899, Toronto. 

 || U.S.G.S. Bull. 180, 1901. 



