A NEW BRITISH ROCK. BY T. BARRON 93 



blue mineral to riebeckite. The following 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 Verrier ;^ and in a rock of the same description from 

 Colorado by Lacroix.^ In 1891, Mr J. J. H. TealP recorded the 

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

 The following year it was described in a granitite from Southern 

 Sikhim, India, by Mr T. H. Holland.^ 



Eiebeckite has also been described by Professor Grenville 

 A. J. Cole,^ from eurite-pebbles collected from the glacial drift 

 of the Isle of Man and Moel-y-Tryfaen ; and later at Greenore,® 

 near Carlingford, Ireland. Professor Solas'' has also described 

 it from the glacial drift at Greystones, 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 re- 

 corded. 



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 Geolog- 

 ical 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 striae 

 on the rocks of the Black Hill. But the lava has not only been 



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



* Op. cit., p. 39. 



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



* Records, Geol. Survey of India, vol. xxv., pt. 3 (1892.) 

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



^ Nature, vol. xlvii., p. 464. 



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



