110 MB. K. H. WORTH OIS' THE [vol. lxXV, 



of the felspar, due to an action which has been without influence 

 on other of the felspar-crystals. 



Montmonllonite is not wholly confined to the coarser veins, for 

 a rare example of the normal rock can be found suffused by a rose 

 tint, and becoming almost wholly rose-coloured along certain 

 planes ; in these specimens the unaltered felspars are more than 

 usually fresh. Yet other instances occur, in which some of the 

 felspars of the fine-grained rock have assumed a rosy colour, but 

 retain their hardness unimpaired. 



Alteration to montmorillonite is not the only disease that has 

 attacked the felspars of the coarser veins. At one point in the 

 quarries, and so far at one only, some of these crystals were found 

 converted into a rather sandy, friable, yellow substance, while still 

 retaining traces of the original cleavages. 



Axinite. — This, so far as the aplite is concerned, occurs only 

 at the contact with the sedimentary and ' dark igneous ' rocks. The 

 crystals are pale brown or violet, and of the characteristic form. 

 When found the mineral is freely developed, but it is of rare 

 occurrence. There is always a little associated fluorspar, and 

 occasionally some dark tourmaline. 



The Minor Aplite- Dykes. 



Excepting the offsets at LXXVI, S.E. 19-64-65 and 23, and a 

 few trivial veins, there is no aplite north of the main dyke. The 

 offsets mentioned are petrologically identical with the main mass : 

 23, near the Redaven, was quarried into, under the belief that it 

 was a part of the principal mass ; it was found to be 7 feet wide, 

 yielded some of the best specimens of green tourmaline, and 

 terminated abruptly north-eastwards in a square end against the 

 shale. At some time 3 9 has also been quarried. 



A narrow vein of aplite occurs in the shale at LXXVI, S.E. 18, 

 about 200 feet south-east of Quarry I. A little below the Kedaven 

 mine a dyke crosses the stream ; it is 3 feet S inches wide, and 

 at this point appears to be a sill, conforming to the dip and strike 

 of the shales. This is at LXXVI, S.E. 27. 



About 170 feet south of the confluence of the eastern tributary, 

 another d} T ke crosses the stream, LXXVI, S.E. 29 b. This appears 

 again in the bed of the tributary at LXXVI, S.E. 51, and 

 between this and LXXVI, S.E. 52, three other courses of aplite 

 appear in the bed of this tributary; the belt may be treated as 

 being a single intrusion, which lies within the limits of the 

 aluminous shales. At LXXVI, S.E. 52, the aplite passes at its 

 margin into schorl-rock, the only instance found in any of these 

 dykes. The felspars become much clouded as the schorl-rock is 

 approached, and needles of blue secondary tourmaline penetrate 

 them. The schorl-rock itself consists of tourmaline and quartz 

 only ; the quartz shows large cavities, many with fluid and a 

 bubble, and a fair proportion containing a cubic crystal also. 



That LXXVI, S.E. 27 is a belt of rock which extends north- 



