372 T. Barron — A British Rock containing Ncpheline, etc. 



hornblende from Mynydd Mawr, Carnarvonshire," which resembled 

 the Socotra mineral very closely in its general characters. He, 

 however, referred it with some hesitation to arfvedsonite. In the 

 same year Mr. A. Harker, 1 who had been studying this same rock 

 independently, referred the blue mineral to riebeckite. The fol- 

 lowing year two other localities were added to the list of places in 

 which it occurs. It was described in a granulite from Corsica by 

 M. Urbain Le Yerrier; 2 and in a rock of the same description from 

 Colorado by Lacroix. 3 In 1891, Mr. J. J. H. Teall 4 recorded the 

 occurrence of riebeckite in a micro-granite from Ailsa Craig. The 

 following year it was described in a granitite from Southern Sikkim, 

 India, by Mr. T. H. Holland. 5 



Riebeckite has also been described by Professor Grenville A. J. 

 Cole, 6 from eurite-pebbles collected from the glacial drift of the 

 Isle of Man and Moel-y-Tryfaen ; and later at Greenore, 7 near 

 Carlingford, Ireland. Professor Sollas 8 has also described it from 

 the glacial drift at Grey stones, co. Wicklow. 



The object of this present paper is to add one more locality to the 

 list of places from which riebeckite has been recorded, and to 

 describe a rock in which nepheline is associated with riebeckite — 

 a combination which has not hitherto been recorded. 



Occurrence in the Field. 



The area from which the rocks to be described were collected, 

 may be seen by referring to quarter- sheet No. 25 of the Geological 

 Survey of Scotland. The specimens were obtained from three hills 

 in the valley of the Tweed, two of which (the Eildons) lie to the 

 west, and the other (Black Hill) lies to the east of that river. 

 Viewed from the east, these three hills stand out boldly from the 

 surrounding country, forming a conspicuous landmark. They are 

 isolated pieces of what was once a continuous mass of lava, which, 

 by the action of disintegrating agents, has been cut into ridges 

 having a general trend east and west. That ice has played an 

 important part in the configuration of this district, may be seen 

 by a glance at the disposition of the ridges and valleys; and as 

 confirmatory evidence I have found glacial strias on the rocks of 

 the Black Hill. But the lava has not only been cut into ridges 

 lying east and west ; it has also been breached by the Tweed in 

 a southerly direction. In this way the Eildon Hills have been 

 separated from the rest of the mass. The eastern side of the Tweed 

 valley is formed at this point by the escarpment of the Old Ked 

 Sandstone, capped by igneous rock ; and it is part of this escarp- 

 ment which forms the base of the Black Hill. The opposite side of 



1 Geological Magazine, Decade III, Vol. V (1888), p. 455. 



2 Comptes Rendus de Acad, des Sciences, tome cix (1889), p. 38. 



3 Op. cd., p. 39. 



4 Mineralogical Magazine, vol. ix (1891), p. 219. 



5 Records, Geol. Survey of India, vol. xxv, pt. 3, 1S92. 



6 Mineralogical Magazine, vol. ix (1891), p. 222. 



7 Nature, vol. xlvii, p. 464. 



8 Proc. Geol. Assoc, vol. xiii (1893), p. 118. 



