36 PBOF. T. G. BONNET ON THE [Feb. 1 896, 



bands consist of a very pale green serpentine thickly speckled with 

 opacite or streaked with clusters of the same substance ; the lighter 

 of the orange-coloured serpentinous mineral, mentioned above, of a 

 colourless, but rather ' dirty ' pyroxene, 1 and of barely translucent 

 brown granules, in part at least iron oxides, more or less hydrous. 

 In short, this rock in parts closely resembles the serpentinous 

 portions of the Potstone Point specimen. 2 I have also examined a 

 specimen of the hornblende-schist in contact with the serpentine. 

 The fragment — from the face of the mass on the left hand of the 

 figure — is about an inch thick. Beginning with the part farthest 

 from the other rock, we find a band from J to ^ inch broad, which 

 exhibits a gran alar structure like that of an ordinary hornblende- 

 schist, the hornblende being roundish in outline and brown in 

 colour, and the other grains composed of an ' earthy ' material, no 

 doubt replacing felspar, which, indeed, here and there can be 

 recognized. A thin lighter-coloured band succeeds, still containing 

 grains of brown hornblende, but with a more fibrous structure in 

 the intervening material. This is followed by a generally similar 

 layer, in which, however, the hornblende-grains are paler in 

 colour, though, with the polarizer, they exhibit a brown pleo- 

 chroism. In the remaining part of the slide (about J inch) the brown 

 colour of the hornblende-grains is less conspicuous, and they are 

 sometimes embedded in a pale-green fibrous mineral. The interval, 

 in short, between the grains everywhere appears to be a variable 

 mixture of minute minerals, of a more or less fibrous habit, among 

 which I think actinolite and serpentine may be recognized, and 

 near the very edge, where the grains of hornblende become less 

 frequent, are dull orange-coloured patches, perhaps only staining, and 

 the rock becomes more definitely fibrous. Granules of iron oxide, 

 as might be expected, occur here and there in the slice. 



Another specimen, from a part of the adjacent hillside, where 

 the serpentine appears to have forced its way between two slabs of 

 hornblende-schist and to include a little streak of the latter, is very 

 interesting. This streak is about an inch thick, and the slice has 

 been cut through it (PI. I. fig. 2). Beginning on one side we find 

 a greenish, orange- coloured serpentinous mineral, in which are 

 scattered more or less acicular microliths of a colourless hornblende. 

 As these microliths increase in number, the former mineral is re- 

 placed by a more or less distinctly fibrous one, though the transition 

 between the two kinds of rock is rather abrupt, as in the case of 

 fluxional streaking ; then comes a brownish hornblende, rather more 

 granular in habit, associated with a colourless mica-like mineral, 

 probably a chlorite. Lastly, the hornblende-grains, still generally 

 composite in structure, but becoming larger and more definite, are 

 parted by earthy spots like the residue of felspar, and from this 



1 Probably white hornblende, for the mineral occurs in all the serpentine of 

 this neighbourhood. 



2 The specific gravity is 2*539, that of the Predannack serpentine, as 

 already stated, being 2 - 766, but the difference is probably due to decom- 

 position. 



