119 



I. From serpentine near the Black Dog, Aberdeen. Trans. Roy. 

 Soc. Edin., Vol. XXVIII., p. 500. 



II. From serpentine, Balhammie, Ayrshire. Trans. Roy. Soc. Edin , 

 Vol. XXVIII., p. 494. 



Auyite (Dialhtyc) . A monoclmic pyroxene has been observed by 

 Professor BOMXEY in some varieties of the Lizard serpentine. It appears, 

 however, to be much less abundant than either olivine or enstatite, and was 

 doubtless entirely absent from large masses of the mother-rock of the 

 serpentine. 



Hornblende. This mineral is of considerable interest, and occurs very 

 abundantly in certain varieties of the Lizard serpentine. The serpentines 

 with hornblende differ, as a rule, in a marked manner from those which do 

 not contain this mineral. They are dark in colour and often exhibit a banding 

 due to variation in the relative proportions of the constituent minerals. The 

 veins and blotches of colour which give such a marked character to the 

 serpentines without hornblende, are usually absent from the rocks which 

 contain this mineral in abundance. On fractured surfaces the hornblende 

 may be recognised by the small bright cleavage faces. As a rule the crystals 

 are minute, but sometimes they measure an eighth or even a quarter of an 

 inch in length. 



In thin section the hornblende is usually seen to be colourless or 

 a very pale green. Sometimes indications of a brown tint may be observed. 

 It occurs in irregular grains, elongated in the direction of the vertical 

 axis. The cleavage cracks are well marked and highly characteristic. 

 The maximum extinction in the prismatic zone is about 20. This horn- 

 blende appears to be similar to that of certain Norwegian peridotites, 

 to that of the Rauenthal serpentine, described by WEIGAND, and to that 

 of certain serpentines from Erbendorf in Bavaria described by SCHULTZE. (1) 

 It belongs to the grammatite variety and passes over into serpentine in 

 the manner described by WEIGAND and SCHULTZE. (See ante p. 111.) 



In addition to the hornblende above referred to, which appears to have 

 formed a constituent of the mother-rock of the serpentine, we find also in 

 certain veins a colourless variety which takes the form of long prisms 

 (tremolite), often grouped in a more or less radial manner. This variety 

 must certainly be of secondary origin. 



Felxpar. This mineral is very rare in the serpentines. Professor 

 BONNEY records it as occurring at Gue Graze in the Lizard district. It is 

 present also in slides of a variety of serpentine from the Rill Head, near 

 Kynance, lent to the author by Mr. WALLER. It occurs in irregular grains 

 which show the characteristic twinning on the albite plan. The angle 

 between the extinction positions of two adjacent lamellae which gave 

 approximately symmetrical extinctions was 53 ; a fact which shows that the 

 species must be allied to bytownite. (2) 



(1) Z.D.G.G., Vol. XXXV., p. 433. 



(2) The author has recently visited the district and asertained that serpentine containing 

 felspar forms a large portion of the Rill Head. The original rock was. therefore, of the nature 

 of a picrite. 



