PRODUCTION OF APPARENT DIORITE BY METAMORPHISM 685 



to other rocks are: (1) its grading or merging into the inclosing rocks; (2) its 

 occurrence only in graywacke, feldspathic gneiss, highly altered f eldspathic 

 sandstone, or metamorphic rocks of that general composition; (3) its small 

 dimensions, its thickness rarely as great as 3 feet; (4) the absence of any re- 

 lated or similar igneous rock in the regions marked by the occurrence of the 

 "diorite" bodies; (5) its presence in rocks of this composition at many Cam- 

 brian and pre-Cambrian horizons ; (6) its occurrence in these small bodies over 

 many thousands of square miles. 



Mineralogically the "diorite" consists of quartz, hornblende or biotite, garnet, 

 albite and oligoclase, zoisite, titanite, and sulphides, generally in this order of 

 abundance. These are arranged so that the new minerals replace the struc- 

 tures and minerals of the inclosing rocks, and usually have a random arrange- 

 ment of their prisms in strong contrast with the schistosity of the older rocks. 

 This is quite marked where the minerals of the "diorite" merge into the gray- 

 wacke or are formed, as often happens, in patches or single crystals outside of 

 the main part of the "diorite." The most striking form of "diorite" is a sphe- 

 roidal or ellipsoidal ball from a few inches to a foot or so in diameter, replac- 

 ing graywacke. These forms consist of a series of shells of different mineral 

 composition, some balls having six or seven shells plainly shown. 



The conclusion is reached that the "diorite" results from static metamor- 

 phism of the graywacke or similar rock under intense pressure, but with 

 scarcely any differential motion. For lack of a suitable term, pseudo-diorite is 

 the best for present use. These occurrences raise anew the question of the 

 formation of igneous rocks from sediments by fusion, for these pseudo-diorites 

 have the characters of igneous rocks and are plainly derived from sediments. 

 It appears in them, however, that it is not mass fusion which is responsible for 

 their production, but mineral recrystallizatlon by solutions under pressure. 



MEDIA OF HIGH REFRACTION AND SOME STANDARD MEDIA OF LOWER 

 REFRACTION FOR THE DETERMINATION OF REFRACTIVE INDICES WITH 

 THE MICROSCOPE 



BY H. E. MERWIN 1 



(Abstract) 



By weighing out and fusing together definite proportions of two or more 

 suitable substances, immersion media, which become fluid by gentle heating, 

 can be prepared, which remain permanently standard and cover practically the 

 whole range of refractive indices of minerals. Fluid media covering the range 

 1.74 to 2.2 can be made from methylene iodide and its compound with arsenic 

 trisulphide. 



CERTAIN SO-CALLED METEORIC IRONS OF CANTON DIABLO 

 BY CHARLLES R. KEYES 



(Abstract) 



The great abundance of so-called meteoric iron found in the vicinity of 

 Canyon Diablo, Arizona, has been pointed to as affording strong evidence of a 



1 Introduced by Fred E. Wright. 



XLVII — Bull. Geol. Soc. Am., Vol. 24, 1912 



