J. J. H. TeaU—Nej)heUne-Sfjenite in N. W. Scotland. 389 



leucite. Those specimens -wbich have been collected frequently 

 show polygonal outlines strongly suggestive of icositetrahedra, and 

 it is highly probable that more perfect forms will be found. The 

 groundmass of the leucite-syenite consists principally of eleolite, 

 black garnets, and orthoclase. A green pyroxene, biotite, and 

 sphene are also present. Melanite, according to Williams, " is found 

 in varying quantities in the different specimens. In some it is almost 

 entirely wanting, while in others it forms a very important factor. 

 It is of a rich brown or yellowish-brown colour, decidedly zonal 



in its structure, and isotropic in its optical properties 



In some cases more than half the area inclosed within the boundaries 

 of the section consist of melanite material." 



This description leaves no doubt that those portions of the 

 ' leucite-syenite ' of Magnet Cove in which melanite is moat 

 abundant are practically identical with the borolanite of Assynt. 

 This conclusion is confirmed by a comparison of the chemical 

 analysis of the borolanite dyke discovered by Mr. Gunn with that 

 of the rock described by Williams. 



I. II. 



SiOj 47-8 50-96 



Alj O3 20-1 19-67 



Fez O3 6-7 7-76 



FeO -S 



Mg 1-1 0-36 



CaO 5-4 4-38 



Na2 6-5 7-96 



K2O 7-1 6-77 



HjO(Ig.) 2-4 1-38 



Ti02 -7 -52 



SO3 -4 



MnO -5 tr. 



BaO -8 



CI -25 



99-3 100-01 



I. Borolanite dyke, Camas Eilean Ghlais. Analysis by Player. 



II. ' Leucite-syenite,' Magnet Cove. Analysis by Noyes. 

 Another rock somewhat allied to borolanite is the ijolite of 



Eamsay and Berghell.^ It is essentially composed of nepheline, 

 pyroxene, and a titaniferous melanite (jiwaarite).'^ 



In addition to borolanite there are some other interesting 

 modifications of the syenitic magma, apparently detached from the 

 main mass, near Ledbeg at the contact with the marble. One of 

 these (4,288) is a dense, dark-green rock, composed of a green 

 pyroxene and orthoclase or moire-microcline with sphene as an 

 important accessory ; another (3,088), also dark in colour, is 

 composed of fegirine-augite, orthoclase, pseudomorphs after idio>- 

 morphic nepheline, and rich brown sphene. Both are augite-syenites, 

 one containing nepheline and the other not. 



' "Die Gesteine von Jiwaara in Finland " : Geol. Foren. Stockholm Forandl., xiii, 

 (1891), p. 300. 



* It is quite possible that some varieties of the melanite of tho borolanite may be 

 titaniterous, but in order to prove this the material analyzed would have to be very 

 carefully examined under the microscope, as the mineral is not unfrequently crowded 

 ■with minute inclusions of sphene. 



