part 2] GEOLOGY OF THE MELDON VALLEYS. 107 



with occasional blue tints is the colour in all the minor dykes. 

 Portions of the emerald-green crystals are sometimes of a fine 

 bright blue. The late K. N. Worth recorded the pink form, 

 rubellite (6) : this was an instance of close observation combined 

 with good luck ; the amount open to his inspection was but small, 

 and in nine years' development of the quarries I have only found 

 one block that contains rubellite. The colour is a fine clear ruby, 

 and rarely extends over the whole of a crystal. In some instances 

 one end of a crystal is red and the other end colourless. Some 

 crystals are red in the central third of their length, green at each 

 end, and colourless between the red and green. The specimen, 

 which comes from one of the coarser veins, contains emerald- 

 green, blue, red, and colourless tourmaline. 



At the junction with the sedimentary rocks there is sometimes a 

 slight development to black schorl, cinnamon-brown to indigo in 

 section (Q. III. GO) : this is occasionally associated with axinite 

 i Q. Ill, 36), and the tourmalines are zoned in brown and indigo, 

 the brown forming the core. At junctions with the igneous inclu- 

 sion (Q. Ill, 76) tourmaline is frequently developed, some crystals 

 crossing the junction ; this mineral in the inclusion is golden brown, 

 in the aplite near the junction it is blue, and where a crystal is 

 common to both its ends vary in colour. Away from the actual 

 contact there are slight patches of blue in the inclusion-tourmalines, 

 and some golden-brown crystals with outer zones of blue in the 

 aplite. 



In the normal rock tourmaline occurs in irregular grains and in 

 prismatic forms, a fair average for the larger of the latter would be 

 0-50 mm. by 0*25 mm. The prisms are usually somewhat ragged 

 at the ends. The grains are pitted and perforated by inclusions, 

 many of which are certainly quartz. Parallel growths of tour- 

 maline and topaz occur: as. for instance, in Q. I, 71, where a topaz- 

 crystal and a tourmaline have grown side by side with the same 

 elongation and extinguish together. 



In LXXVI, S.E. 27, a dyke crossing the Redaven above the 

 quarries, rather long needles of tourmaline occur as inclusions in 

 topaz, and are so oriented as to extinguish simultaneously with 

 that mineral. On the other hand, in LXXVI, S.E. 38 (base of 

 Homerton Hill) the pale-brown tourmalines frequently enclose 

 topaz in parallel growth ; in this slide and this only the tourmaline 

 sometimes takes on a blue tinge at the contact with the topaz. 



Tourmaline is frequently moulded upon felspar, as in Q. I, 25 

 (PL VII, fig. 16), especially upon the plagioelase-laths : the figure 

 shows two patches of tourmaline, both belonging to the same 

 crystal, divided by a felspar which itself is a Carlsbad twin. But 

 the mineral very rarely occurs us inclusions in felspar. On the 

 other hand, in LXXVI, S.E. 20 (South Down Quarry) tourmaline 

 occurs in ophitic plates enclosing felspar-laths. 



The mineral is often in close association with apatite. Zoning 

 and local coloration are common, especially in the olive-green 

 variety, the centre of the crystal being the darker, except in rare 

 instances. 



