136 



Individual flakes may be as much as 1 mm. by 5 mm, 

 Ilmenite in small grains is scattered through the aggregates 

 just as it is through the groundmass. In these chlorite- 

 muscovite aggregates the chlorite is usually central, and 

 the muscovite peripheral, though there is a good deal of mutual 

 penetration. 



Between the two extreme types of aggregates described 

 above there are numerous transitional types in which the 

 grainsize is intermediate between the limits given, and the 

 amount of quartz and biotite varies also. The aggregates 

 run up to about 2 mm. diameter. 



In addition to these aggregates there are also some in- 

 dependent porphyritic crystals of clinochlore about *4 mm. 

 by '05 mm. These possess characters exactly similar to 

 those described in the preceding rock. (Plate ii., fig. 3.) 



Wynyaed, Blakiston. ScapoJite amphibolite. — The 

 rock consists essentially of actinolite and scapolite. The struc- 

 ture answers admirably to the description of jooikilohlasfic 

 structure given by Grubermann. 



Actinolite is the most abundant constituent. At first 

 sight it appears to be irregularly scattered about in stumpy 

 rods, here and there aggregated into masses. The masses 

 are, however, crystal grains, and the surrounding rods are in 

 optical continuity with them. The optical orientations of 

 adjacent areas are quite independent, and are in no w^ay 

 determined by the schistosity of the rock. 



The scapolite is perfectly colourless, and forms a base 

 in which the actinolite is scattered. It is optically continuous 

 over wide areas whose boundaries are extremely irregular. 

 The refractive index is notably greater than that of Canada 

 balsam, and the double refraction quite strong. The mineral 

 is uniaxial and negative. There is little trace of cleavage, 

 and the mineral is remarkably fresh. In places there is a 

 tendency towards fibrous structure, probably pointing to in- 

 cipient decomposition. Adjacent fibres show marked differ- 

 ences of double refraction. When the lengths of the fibres 

 are parallel to the plane of vibration of the light no Becke's 

 effect is noticeable between them, but when they are rotated 

 through a right angle marked differences of refractive index 

 are apparent. 



Biotite pleochroic in red-brown to light yellow tints is 

 abundant locally through the rock. There is plenty of grey- 

 ish sphene in small fusiform grains. Fine iron ore is scat- 

 tered through the rock, particularly in the actinolite. 



Wynyaed, Blakiston. (This rock and the preceding 

 one are from a well.) Amphibolite. — The rock is somew^hat 



