No. 2306. CUMBERLAND FALLS METEORITE— MERRILL. 99 



of the monoclinicform as indicated by the amount of alumina and Hme 

 (1.09 AI2O3 and 0.96 CaO) must be very small. The extreme nar- 

 rowness of the bands giving the inclined extinction is, however, at 

 least partially confirmatoiy of this. 



The chalky appearance of the mineral is plainly due to its physical 

 condition, an abnormal development of the cleavage, which inciden- 

 tally causes it to crumble away under slight pressure and makes it 

 susceptible of being ground to powder in an agate mortar as readily 

 as so much calcite. Whether this condition is due to the shock which 

 resolved the original mineral into fragments is uncertain, but it would 

 seem most probable. The failure to become recompacted under 

 subsequent pressure might well be ascribed to a lack of moistm-e, 

 pressure and dry heat alone naturally bemg less conducive to meta- 

 morphism. 



In addition to the above, certain of the slides show intergrown 

 with the enstatites in the form of small oval and irregular areas a 

 brilliant polarizing mineral with the sharply developed platy struc- 

 ture characteristic of diallage. The mineral is also nearly colorless 

 with a very faint green tinge, and gives extinction angles measured 

 against the edges of the plates, that is, on clino-pinacoidal sections, 

 as high as 27°. The proportional amount of the diallage is quite 

 variable, some slides showing only an occasional rounded granule and 

 others several of the intergrowths mentioned. 



Scattered irregularly throughout the mass of the rock are the scale- 

 like segregations of graphite above noted, sometimes several milli- 

 meters in diameter, in connection with which a differential movement 

 has given rise to small areas with slickensided surfaces. In the finer 

 portions, the graphite is so evenly and finely diffused as to impart 

 a dark gray color. Metallic particles are quite inconspicuous except- 

 ing on a polished surface, as are also those of iron sulphide. The 

 relatively greater abundance of the metal and sulphide in the dark 

 inclosures above noted, is very evident on the polished surface 

 (pi. 18). No calcium phosphate, maskelynite, oldhamite, osbornite, 

 or other accessory minerals can be detected, although microchemical 

 tests give rise to the usual globular ammonium-phospho-molybdate 

 forms. 



A close study of the dark inclusions developed some interesting 

 and unexpected conditions. Examination with a pocket lens of the 

 polished surface of one of the larger inclosures shown in plates 15 and 18 

 at once suggests a chondritic structure, a suggestion fully borne out 

 by a study of the material m thin section, which shows a dark, obscure, 

 and muddy ground containmg numerous illy defined, compressed and 

 distorted radiating, barred, and nearly holocrystalline chondrules 

 of olivine and enstatite, mostly so obscured by a black impregnation 

 that their true mineral nature is scarce recognizable. In these respects 

 the structure so closeh' resembles that of the McKirmey and Travis 



