92 



On a New British Rock containing Nepheline and 

 Riebeckite. By T. Barron, A.R.C.S. (Plate V.) 



The Rev. George Gicnn thinks it opportune to reprint the followitig 

 paper on the Geology of the Eildons and the Black Hill., %vhich 

 was published in the Geological Magazine., August i8g6, and 

 is obliged to the author., Mr Thomas Barron., F.G.S., for his 

 cofiseftt. 



Introduction. 



The mineral riebeckite was first discovered by Professor 

 T. G. Bonney^ in 1882, who in a paper to the Eoyal Society 

 describing a series of rock-specimens from the island of 

 Socotra, noticed the occurrence in a granite of a mineral 

 which, though presenting characters common to the hornblende 

 group, he referred doubtfully to tourmaline. 



Four years later Oebbeke^ described a mineral from the 

 island of Sikoku, Japan, which showed intense colour and 

 pleochroism, but differed in other respects from glaucophane, 

 to which he referred it. The following year Professor A. 

 Sauer,^ of Leipzig, in examining a series of specimens 

 collected by Dr E. Riebeck from the island of Socotra, noticed 

 the blue mineral described by Professor Bonney. Having 

 isolated and analyzed it, and determined its optical properties, 

 he placed it among the amphiboles, naming it riebeckite. 

 In the same year Eosenbusch^ found a peculiar variety of 

 hornblende in a syenitic lamprophyre, which agreed in its 

 optical properties with the mineral described by Saner. 



In 1888 Professor Bonney^ described a "peculiar variety of 

 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," who had 

 been studying this same rock independently, referred the 



1 Phil. Trans., vol. clxxiv. (1883) p. 283. 



=" Zeitschr. fiir Kryst, vol. xii. (1886) p. 285. 



3 Zeitschr. der Deatsch. geol. Gesellsch, vol. xl. (1888) p. 138. 



* " Die massige Gesteine," Bd. ii. (1886-7) p. 312. 



* Mineralogical Magazine, vol. viii. (1888) pp. 103, 169. 



^ Geological Magazine, Decade III., vol. v. (1888) p. 455. 



