86 MB. B. H. AVOETH OX THE [vol. lxxv r 



of alteration. In fibrous form it frequently fills cracks in the 

 shale, the fibres extending from side to side of the crack. Layers 

 10 mm. and more thick are thus formed, which part readily from 

 the walls of the crack and can be obtained as small slabs. The 

 only other mineral certainly present is pyrite in an occasional 

 grain, but there seems some reason to believe that a little 

 pectolite may also occur. (Very fine specimens of pectolite in 

 radiate form have been found in the L. <v_ S.W, Railway quarry.; 

 Wollastonite also occurs intergrown with idocrase. 



Axinite is confined to the immediate neighbourhood of the 

 junction. In colour it is a very light purple-brown, the crystals 

 being clear and transparent. It is associated with dark tourmaline, 

 with fluorspar, and with epidote. Axinite is also found in the 

 rocks north of the Meldon aplite-dyke, by the Eedaven ; it is 

 there rather dark brown, and its origin may be connected with a 

 vein of the ' dark igneous ' rock. 



Lepidolite is a mineral of the inclusions rather than of the 

 contact-rocks. The smaller inclusions, the mere broken fragments 

 some few inches in diameter, which have been torn off from the 

 shales and wholly surrounded by the Meldon aplite, in their 

 fullest alteration acquire a horny texture and lustre. They cleave 

 readily, the cleavage-surfaces beino* curved and waved and having 

 a satiny sheen. The colour is brown- grey, with a slight silvery 

 lustre. The material is translucent. A modification occurs, which 

 is intermediate between this texture and porcellanite. The whole 

 rock fuses readily at the edges of chips in the bunsen burner, and 

 gives a strong lithiimi flame. 



To the naked eye sections appear as practically clear glass, 

 if cut parallel to the cleavage (Q.I, 28) : they show no structure 

 under the microscope, except between crossed nicols, but then 

 appear as a rather irregular mosaic of small grains polarizing in 

 grey tints, with occasional blades and grains giving fairly high 

 colours. Omitting for the moment certain subsidiary minerals 

 present in small quantity, the rock is an aggregate of flakes of 

 lepidolite arranged with their cleavages almost uniformly parallel : 

 hence the low tints of the majority of the grains which are viewed 

 normal to the base (Q.I, 28) [PL V, fig. 5]. Cross-sections at right 

 angles to the cleavage of the rock show a blade-like form of the 

 grains : the whole section is low in tint between crossed nicols when 

 the direction of cleavage of the rock is parallel to either diagonal, 

 and shows only spots of high colour ; but at the 45° position, it 

 takes on high tints, which are uniform over wide belts, and show 

 only a few spots of lower colour (Q.I, 68). Grains of apatite 

 and needles and grains of green tourmaline occur as accessories. 



In Q.I, 45, which shows a junction of the Meldon aplite and 

 one of these inclusions, the inclusion farther from the aplite 

 contains an occasional small crystal of green tourmaline ; nearer the 

 junction there is much pale-blue apatite in small grains. Still 

 nearer the junction, granular aggregates of tourmaline become 

 abundant, and the mica passes to a distinctly coarser form. The-- 



