ANDESITES OE DEVONSHIEB. 507 



is much of the iron ore in the rest of the rock. Although some of 

 the felspar is undoubtedly plagioclase, I am uncertain whether it is 

 all so. 



(c) Mica-augite-andesite of Killerton. 



This rock would be termed mica-augite-porphyrite by Rosenbusch. 

 I can hardly describe it better than by saying that it looks like a 

 minette, but is lighter in colour than most minettes. Specimen 

 Ko. 907 is very micaceous, and the abundant small glistening flakes 

 of mica have the same brown colour as the compact groundmass. 

 Specimens Nos. 900, 901 are bluish to purplish grey and contain 

 the same brown mica much less abundantly. Specimen No. 902 is 

 light purplish grey, with comparatively few visible flakes of mica and 

 numerous small narrow elongated cavities. Sp. gr. 2'57. 



Phenocrysts occur of augite, brown mica, apatite, and iron 

 ores. Groundmass of felspar. 



The augite phenocrysts are almost colourless or faintly greenish, 

 0-5 millim. in diameter or smaller, and are often partly altered to 

 calcite. Brown mica is abundant. In one case it was included in 

 the augite. On the other hand it frequently contains apatite and 

 iron-ore inclusions. Apatite occurs in numerous small crystals, and 

 iron ore is generally distributed. 



Mr. Edward Haworth has kindly made for me in the Chemical 

 Laboratory of Owens College the following analysis (A) of the rock, 

 m. 900 :— 



SiO, 



AlA 



FeA 



FeO 



MgO 



CaO 



NagO 



K^O 



H^O 



P2O5.. 



CO, 



10066 99-99 



It is evident from analysis (A) that the felspar of the groundmass 

 is plagioclase. The analysis (B) is that of the Morpeth dyke, Mor- 

 peth, Northumberland, by Mr. Stead, of Middlesbrough, quoted from 

 Teall, 'British Petrography,' 1888, p. 206, for comparison. 



A. 



B. 



. 48-37 



51-20 



, 20-74 



20-03 



6-561 

 -63/ 



7-57 



6-35 



6-75 



7-77 



10-52 



1-70 



1-71 



— 



0-51 



1-60 



1-70 



-94 







600 



— 



Q.J.G.S. No. 192. 2n 



