408 EEPORT— 1888. 



converted into the talcose material, which is mostly in fibres, but occa- 

 sionally has a fragmental form with diallage cleavages. This material 

 is in porphyritic patches. The remainder is partly mosaic felspar and 

 partly epidote, the latter in patches which are obviously cracked, drawn 

 out, and separated. Thus our eyed gabbro has become a talcose epidote 

 schist. Here, however, the original positions of the diallage crystals are 

 still indicated, so that the rock at Penrhyn Fadoc (49) is a still further 

 stage. In this epidote is very abundant, but it occurs not only in pulled- 

 out bands, but in scattered recrystallisations lying in clusters in a 

 groundmass of the talcose fibres. The freedom of certain spots from 

 these new crystals is the only indication of where diallage has originally 

 been, except that by good fortune one or two small fragments of the 

 unaltered mineral are actually left. Finally, in the rock in the railway 

 cutting (50) (see fig. 23) there are whisps of talcose fibres, like cirrus 

 clouds, flashing out on a dark background, consisting of broken and 

 drawn-out fragments of epidote, now ground to opaque dust or partially 

 recrystallised to form mosaic felspar. 



These igneous mylonites, whose origin is thus demonstrated, however 

 schistose they may be, nevertheless difier entirely from the neighbouring 

 schists of the island both in their chemical constitution and in the 

 character of the orientation that affects them. For this reason it is 

 probable that the soapstone at PwU Clai (54) is not an altered schist, 

 but is derived from the decomposition and recrystallisation of one of the 

 gabbro group, in association with which it occurs. It consists, like the 

 last described, of talcose fibres, small mosaic felspar, and a few epidote 

 crystals ; but it is much cleaner, and though it has been a mylonite by 

 the general arrangement of its lines, it has since that time recrystallised. 



Of the serpentines, the most typical observed is from the base of the 

 first inlet south of Four Mile Bridge (51). In this the original crystals 

 of olivine can still be seen in outline in certain parts, floating in a 

 transparent matrix, which is of apparently later origin. Fitting in with 

 these in a holocrystalline manner are several areas showing the fine 

 fibrous cleavage structure of enstatite. The ferric constituent is not> 

 found distributed in the cracks, but occurs chiefly in the form of 

 rounded masses like eroded crystals, or scattered like dust, both in the 

 olivine areas and elsewhere. The alteration of the olivine has taken 

 place along lines which have a tolerably uniform direction throughout 

 the rock, and which pass through the enstatite patches. We may there- 

 fore conclude that they were produced by the general forces which have 

 brought about the foliation of the district, and that the rock is in fact a 

 foliated serpentine, which was once a Saxonite. From the primary lines 

 of alteration in the olivine areas a transverse set of lines has proceeded, 

 so that the whole crystal is changed into a series of broken parallel bands 

 of chrysolite. The enstatite areas, on the contrary, though roughly 

 traversed by the general lines, have their fibres arranged along, and per- 

 pendicular to, the most conspicuous cleavage lines. The intervening 

 matrix must be of later date than the primary alteration, as it inter- 

 rupts the parallel lines ; it is composed of indefinitely small fibres, 

 doubtless serpentinous, which, being arranged promiscuously, scarcely 

 have any effect on polarised light. The whole is re-cracked in many 

 directions, and the new cracks filled with serpentine. The metamor- 

 phosis of the rock does not seem, therefore, to have followed the usual 

 course. 



