178 



MR J. HORNE AND MR J. J. H. TEALL ON BOROLANITE. 



viewed by rays vibrating at right angles to the principal axis, and appears a fiery 

 reddish-brown when viewed by rays vibrating parallel with this axis. 



To remove all doubt as to the identification of nepheline, the following analyses were 

 made : — 





I. 



II. 



III. 



Silica, ..... 



47-8 



47-9 



69-3 | 



Titanic acid, . 















•7 



n.e.* 





Sulphuric acid, 















•4 



n.e. 





Alumina, 

 Ferric oxide, . 















20-1 

 6-7 



21-8 | 

 7-flt-J 



16-8 



Ferrous oxide, 















•8 



n.e. 





Manganic oxide, 















•5 



n.e. 





Baryta, . 















•8 



n.e. 





Lime, 















5-4 



5-1 



39 



Magnesia, 















1-1 



1-0 



•3 



Soda, 















5-5 



5-6 



4-6 



Potash, . 















7-1 



7-2 



1-7 



Loss on Ignition, 



• 











2-4 



2-4 



2-4 

















99-3 



98-6 



99-0 



I. Bulk analysis of the rock. For this analysis we are indebted to Mr J. 



Hort Player. 

 II. Bulk analysis of another sample, by Teall. 



III. Analysis of the part soluble in hydrochloric acid from the same sample as No. II., 

 by Teall. 



DESCRIPTION OF THE PLATE. 



Fig. 1. Typical borolanite from the north-west slope of Cnoc-na-Sr6ine. Magnified 33 diameters. Ordinary 



light. The minerals represented, are melanite, biotite (4) and orthoclase (6). The melanite is seen 



to be idiomorphic with respect to orthoclase and biotite. The felspar breaks up, under crossed nicols, 



into an aggregate of large irregular grains. 

 Fig. 2. A rock essentially composed of orthoclase, pyroxene (3) and biotite, from the base of Cnoc-na-Sr6ine. 



Magnified 28 diameters. Ordinary light. This figure illustrates the general character of the pyroxene 



which occurs in the borolanite. The other minerals represented are orthoclase and magnetite (1). 



Under crossed nicols the individuals of felspar give more or less lath-shaped sections, and are in 



almost all cases twinned on the Carlsbad plan. 

 Fia 3. Another portion of the same rock, also magnified 28 diameters. Sphene (2), pyroxene, biotite and 



felspar are represented. The sphene forms a large ophitic plate, all parts of which belong to one 



crystalline individual. 

 Fig. 4. Portion of one of the white patches occurring in typical borolanite. One mile east of Aultnacallagach. 



This figure illustrates the peculiar micro-pegmatitic structure (8) referred to in the text. 

 Fig. 5. The rock is similar to the one represented in figs. 2 and 3. It does not contain melanite. A portion 



of a large crystal of sphene is represented at the top of the figure. The other minerals are green 



pyroxene, felspar and pseudomorpha after idiomorphic nepheline (7) ? 



* Not estimated. 



t Total iron reckoned as ferric oxide. 



| Silica and insoluble residue. 



