part 2] GEOLOGY OK THE MELDON VALLEYS. 85 



constitute mineral-specimens rather than rock-specimens. Two 

 forms of garnet, idocrase, scapolite, wollastonite, and axinitc have 

 thus been found. 



(larnet, the most striking form, is cinnamon-coloured, clear 

 and transparent ; it occurs both massive and in small well-shaped 

 dodecahedra. The garnet is associated with pure white calcite, 

 wollastonite, and green idocrase ; when present it usually forms 

 the larger part of the rock. 



Dark-grey garnets are also found, in detached crystals set in the 

 altered shale, and confined to certain of the original beds of the 

 rock. The crystals range from 1 to 10 millimetres in diameter, 

 and are very usually surrounded by a thin shell of calcite. The rock 

 in which they occur is always highly charged with carbonate of lime. 



The cinnamon-coloured garnet (Quarry 1, 64) shows faint 

 anomalous double refraction in zones parallel to the crystal out- 

 line: in this slide it is associated with wollastonite and quart/. 



The grey garnet (Q.I, 24) exhibits anomalous double refraction 

 by sectors, and is seen to lie in a matrix of carbonate mosaic. 

 The garnet crystals are usually of sharp outline in part only, else- 

 where they die away into the ground-mass which invades them. 

 The garnet is itself colourless, the grey shade being caused by 

 dusty-black pigment, somewhat sparsely scattered. Irregular 

 patches of brown garnet occur (Q.I, 77) in the same slide, and are 

 frequently developed as a discontinuous border immediately out- 

 side the boundary of the grey crystals (PI. V, fig. 2). 



Idocrase, green, rarely in parts brown, occurs in masses 

 consisting of radiate elongated prisms ; with it are associated 

 cinnamon-coloured garnet, calcite. wollastonite, and in places a 

 little pyrite. A line specimen of idocrase-rock found loose at 

 LXXYI. S.E. 13, shows that this mineral results from the contact- 

 action of one at least of the smaller dykes of Meldon aplite, 

 as well as from that of the main dyke. In section the green 

 mineral exhibits rather frequent partial alteration towards brown 

 shades. Both the garnet and the calcite conform to the figure 

 imposed upon them by the idocrase, and are interstitial minerals, 

 tlu' wollastonite being intergrown with the idocrase. The charac- 

 teristic zoning is well developed — an especially neat example is 

 presented by Dr. Young's slide ' Y..J. I" (PI. V, fig. 3). 



Scapolite is in my experience rare. It was found by Dr. .J. 

 S. Flett (8, p. 17). [ The specimens available are almost pure 

 scapolite-rock, in part granular massive, but with silky bundles of 

 prisms of considerable length (up to 30 mm.). An occasional 

 spot of blue apatite is the only other mineral, except for an infil- 

 tration of manganese. The section Q. I, 65 presents both square 

 and elongated form-, with small grains and crystals of apatite as 

 inclusions. Cross-sections of the scapolite (dipyre) show a narrow 

 outer /.one (PI. V, lig. I). 



Wollastonite is the commonest of the recognizable products 



1 These numerals is parentheses throughout the paper refer to the Biblio- 

 graphical List on i). 77. 



