THE 



GEOLOGICAL MAGAZINE. 



NEW SERIES. DECADE IV. VOL. VII. 



No. IX.— SEPTEMBER, 1900. 



OK-X(3-IIsr.A.31. .A.iaTXGXjES. 



I. — On Nepheline-Stenite and its Associates in the North- 

 West of Scotland. 



By J. J. H. Teall, M.A., F.R.S., Pres.G.S. 

 (Communicated by permission of the Director-General.) 



IN 1892 I described, in conjunction with my colleague Mr. Home, 

 a peculiar rock, essentially composed of ortboclase and melanite, 

 under the name of borolanite.' The type-specimens came from the 

 plutonic mass which lies to the north of Loch Borolan, in Sutherland- 

 shire (1 in. sheet 101). During the preparation of the paper on 

 borolanite our colleague Mr. Gunn discovered two dykes of a closely 

 related rock traversing the Torridon Sandstone in the Coigach 

 district of West Koss-shire. The rock of these dykes was described 

 in an appendix to our paper. It contains nepheline and eegirine, in 

 addition to ortboclase and melanite, and is therefore allied, both as 

 regards mode of occurrence and raineralogical composition, to the 

 Tinguaite group of Eosenbusch ; but as melanite is an important 

 constituent it was classed with the borolanites. 



At the conclusion of our paper we say : " The aflSnities of 

 borolanite ai'e unmistakeable. It is a member of the foyaite (elseolite- 

 syenite) family. The occurrence of melanite as an important 

 accessory in certain rocks belonging to the nepheline-leucite group 

 has long been recognized. In our rock we have melanite raised 

 to the rank of an essential constituent. Borolanite, as we have 

 already shown, is intrusive in the Cambrian rocks of Sutherland - 

 shire. The nearest rocks in any way allied to it are the elaaolite- 

 syenites of the Christiania district, which are also intrusive in Lower 

 Palaeozoic strata." 



Since this paper was written I have had the privilege of visiting 

 the Christiania district, under the guidance of Professor Brogger, and 

 the experience thus gained has been of the greatest service iu 

 a re-examination of the post-Cambrian igneous rocks of the north- 

 west of Scotland — a re-examination rendered necessary by the 

 preparation of the Geological Survey memoir on that district. Some 

 of the results thus brought to light, especially the recognition of 

 true nepheline-syenites, as well as other rocks closely allied to types 

 described by Prof. Brogger in his classic memoirs on the Christiania 



' " On Borolanite: an Igneous Rock intrusive in the Cambrian Limestone ot 

 Assynt, etc." : Trans. Roy. Soc. Edin., vol. xxxvii (1892), pp. 163-178. 



DECADE IV. — VOL. VII. — NO. IX. 25 



