152 TF. Campbell Smith — Borolanife from Ross-shire. 



1890. P. M. Duncan & W. P. Sladen. " Oa the Anatomy of the Perignathic 

 Girdle of D. cylhidrica" : Journ. Linn. Soc. ZooL, vol. xx, p. 48. 



1892. SvEN LovEN. " Echinologica " : Bihang Koagl. Svenska Yet. Akad. Haudl., 

 Bande xviii, Afd. iv, No. i. Stockholm. (Describes jaws oiD. cijlindrica.) 



1909. F. A. Bather. " The Triassic Echiuoderms of Bakony." (Terminology 

 of Echinoid jaws discussed.) 



EXPLANATION OF PLATE VI. 

 Fig. 1. — Side view of the specimen of Discoidea cylindrica in Manchester Museum 



(L. 8806), with the jaw apparatus in situ, x IJ. 

 ,, 2. — Outer surface of a pyramid, A in Fig. 1, the two halves separated along 



the symphj'sis and the tooth forced between them. As found, x 8. 

 ,, 3. — Inner (inter-pyramidal) view of a pyramid, with the incurved extensions of 



the halves of the admedian outer plane at the adoral ends, x 8. 

 ,, 4. — Tooth; side view, x 8. 

 ,, 5. — Inner (alveolar) view of a hemi-pyramid, showing the symj^hysial surface 



and half the dental slide, x 8. 

 ,, 6. — Epiphysis, inter-pyramidal surface, showing rounded prominence for 



articulation with a rotula. x 15. 

 ,, 7. — Portion of the perignathic girdle of this specimen, showing the processes. 



X 3. 



III. — On the Composition of ' Borolanite ' froji Am Meallan, 



EOSS-SHIEE. 



By W. Campbell Smith, Scholar of Corpus Christi College, Cambridge. 



rpHE peculiar garnetiferous rock occurring to tlie east of Loch Borolan 

 \_ seems to have been first noted by Dr. Callaway in 1883, and is 

 described by Dr. Bonney in an appendix to Dr. Callaway's paper. ^ 



The rock was more fully described by Messrs. Home & Teall in 

 1892.- The authors give it the name borolanite, defining the typical 

 rock as an aggregate of orthoclase and melanite. The mineral 

 composition is described, with special reference to the white patches, 

 which consist of an aggregate of orthoclase and a substance which is 

 probably an alteration product of nepheline or sodalite. The occurrence 

 of a turbid mineral in micropegmatitic intergrowth with the felspar is 

 noted, and it is suggested that this is an alteration product of nepheline. 

 The theory that these white patches are pseudo-leucites was suggested 

 by Professor Derby, who compared them to the pseudo-leucites of 

 certain Brazilian rocks. It is also pointed out that borolanite appears 

 to be a member of the elseolite-syenite family. 



An appendix to this paper of Messrs. Home & Teall records the 

 discovery of much decomposed borolanite in the Eilean Dhu Limestone 

 at Elphin, and of two vertical dykes in the Torridon Sandstone at 

 Camas Eilean Ghlais. The dyke is of medium texture and brownish- 

 grey colour. Hand-specimens show melanite and lath-shaped cleavage 

 faces of felspar. Sections show the rock to be composed of an aggregate 

 of orthoclase, nepheline (partly decomposed to a substance giving 

 aggregate polarization), melanite, segirine, and biotite. The melanite 

 is either pale yellow or deep brown, a pale zone often surrounding 

 a dark nucleus. Two bulk analyses were made, one by Mr. Hort 

 Player and the other by Dr. Teall; the latter also analyzed the part 

 soluble in hydrochloric acid, thereby proving the presence of nepheline. 



1 Q.J.G.S., 188.3, vol. xxxix, p. 409. 



^ Trans. Eoy. Soc. Edinburgh, vol. xxxvii, p. 163. 



