Vol. 67.] 



SKCXMER VOLCANIC SERIES. 



193 



border of iron-ores, and often includes grannies of brown sphene 

 (fig:. 7, A. below). A certain amount of quartz in the ground-mass 

 and also enclosing felspar-microlites appears to be original. 



The fine-grained trachytic rock from the North Cliff of Skomer 

 -{andesite of Howard & Small) has been analysed (see Analysis IV, 

 p. 192), and by its high percentage of alkalies evidently takes its 

 place among the trachytes. The high percentage of potash was 

 rather surprising, for, as in the case of the rhvolites, no orthoclase 

 could be detected. The analysis would, however, suggest the 

 presence of 19 per cent, of orthoclase, 46 per cent, of albite, and 

 5 per cent, of anorthite. Chemically, the rock compares fairly well 



A = Albite-trachyte, with pseudomorphs after a rhombic pyroxene ; from Crab 

 Hall Quarry, north of Dale. Slide E 7148, ordinary light. X 25 diameters. 



B = Albite-trachyte, with pseudomorph after olivine. Cliff east of High Point, 

 Marloes. Slide E 7759, ordinary light. X 25 diameters. 



with a soda-trachyte (Analysis V, p. 192) from the Bhongebirge 

 described by Prof. Einne ; but it 'differs considerably from the 

 keratophvres, as represented by Dr. Elsden's ' lime-bostonite ' (Ana- 

 lysis VI, p. 192). 



(c) The Keratophvres. 



If the term keratophyre Avere used in the sense in which 

 Prof, llosenbusch uses it, all the rocks so far described would have 

 been included thereunder ; but it seems undesirable to include rocks 

 which have always been regarded as rhyolites, and rocks which 



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