234 JOSEPH P. IDDINGS AND EDWARD W. MORLEY 



The rock whose analysis is No. i is a light-gray, aphanitic 

 variety from Kali Gillinan near Masin, which contains rather 

 numerous large phenocrysts of leucite, ranging in size from a diam- 

 eter of lo mm. to microscopic dimensions. In thin section they 

 exhibit characteristic polysynthetic twinning, and the index of 

 refraction has been determined by Dr. F. E. Wright to be i . 507 

 for sodium light. Their chemical composition is shown by the 

 following analysis by Morley: 



SiOa 54. 97 



AI2O3 , 22.21 



K2O 19 . 98 



NezO 0.81 



FcjOs 0.61 



MgO o. 26 



CaO 0-49 



H2O- 0.08 



H3O+ o. 56 



99-97 

 The groundmass is minophyric and dopatic with abundant small 

 phenocrysts of leucite, augite, and some minute feldspars. In 

 thin section it is seen to consist of small phenocrysts of euhedral 

 leucite, zonal augite, and numerous zonal crystals of calcic andesine 

 or labradorite in a holocrystalline groundmass composed of leucite, 

 prismoids of greenish augite, anhedrons of magnetite, with prismoid 

 plagioclase and anhedral orthoclase, some of which form narrow 

 shells around the plagioclase, as in some shoshonites. The cal- 

 culated norm shows 38 . 9 orthoclase, 18.3 albite, and 9 . 7 nephelite, 

 whereas the mode, or actual mineral composition of the rock, shows 

 that no nephelite crystallized from the magma, but considerable 

 albite, which appears in the lime-soda feldspar. Readjusted on this 

 basis the rock might contain about i.i orthoclase, 36.2 albite, 

 29.7 leucite, and no nephelite. Owing to the smallness of the 

 crystals in the groundmass an actual measurement of the mode 

 of the rock cannot be made without great difficulty. The rock 

 may be called a vicoite, which is equivalent to a leucite shoshonite. 

 The rock of analysis No. 2 is medium gray, very similar to that 

 of No. I, and occurs on Kali Sekatak near Ragou. The phenocrysts 

 of leucite range in size from 10 mm. downward and in places are 



