Branner and Braokett — Peridotite of Arkansas. 57 



The yellow mica is grown through with little colorless lath- 

 shaped crystals like those in the grounclmass. It has a weak pleo- 

 chroism; 0=- orange or faintly reddish; E= yellow.* In some 

 cases the patches of mica are of a darker color and have a stronger 

 pleochroism : 0=brown; E = light brown, almost yellow (Nos. 

 34 and 36). 



The colorless lath-shaped crystals that make up a large por- 

 tion of the groundmass and penetrate the patches of mica, 

 have an extinction angle as high as 45°, and many of them 

 give lively polarization colors. From their association, 

 appearance, optical behavior and close resemblance to similar 

 crystals found in the groundmass of the Syracuse serpentine 

 (to be referred to later), they are probably augite. They were 

 so considered by Dr. Williams who has kindly examined a 

 section of this rock. 



The yellow grains are scattered all through the groundmass, 

 and are next in importance to the augites, and like them are an 

 original constituent of the rock. They are highly refracting, 

 and stand out well in the slide. In color they range from 

 colorless through yellow to yellowish -brown. In form, some 

 appear as irregular grains, others are diamond-shaped or 

 square. They occur singly or grown together in groups. Very- 

 many have crystalline planes and few or none of them are 

 quite isotropic. They resemble very closely the yellow grain 

 described by Dr. Williams f as occurring in the serpentine 

 (peridotite) from Syracuse, New York, which he found by 

 actual separation and analysis to be perofskite. Mr. J. S. 

 Diller ^ described yellow grains in the peridotite from Elliott 

 County, Kentucky, which they T resemble, perhaps, more closely 

 than they do those described by Dr. Williams. Mr. Diller at 

 first took these to be anatase, but a subsequent separation and 

 analysis showed them to be perofskite also. An unsuccessful 

 attempt was made by the writer to separate the yellow grains 

 by the method of Stelzner§ as recommended by Dr. Williams 

 in his paper on the Syracuse serpentine. But the identity in 

 appearance of the yellow grains in the Pike County rock with 

 those in the Kentucky peridotite which Mr. Diller found to be 

 perofskite after this attempted separation was made, coupled 

 with the fact that by Gooch's method | 0.89 per cent of TiO„ 

 was found in the rock, made it so probable that the mineral was 

 perofskite, that no further attempt at separation was made. 



*(Slide No. 35). Determined by Dr. G. H. Williams, Johns Hopkins Univer- 

 sity. To Dr. Williams thanks are also due for kindness in examining a section of 

 this rock, and for a specimen of the Syracuse serpentine. 



+ This Journal, xxxiv. August, 1887, pp. 140-142. 



% Bulletin of TJ. S. Geological Survey, No. 38, p. 18. 



§ Neues Jahrbuch fur Mineralogie, etc., Beitrage Bd. ii, p. 392. 



| American Chemical Journal, vol. vii, p. 283. 



