230 



Prof. T. G. Bonney. 



smooth. The rock, which is rather decomposed and crumbly, consists 

 chiefly of three minerals : garnet, not quite so large, paler and more 

 pink in colour than the last-named; an emerald-green pyroxene, and a 

 yellowish or greenish-grey, platy to fibrous mineral, suggestive of 

 a second more altered pyroxene. In thin slices the paler and pinker 

 tint of the garnet is very perceptible, as well as the tendency to a 

 rude and generally parallel cleavage. But we find in it, under the 

 microscope, a few microlithic enclosures, of an apparently colourless 

 mineral, which occurs in long prisms crossed at about 70° by an 

 occasional transverse cleavage, and extinguishing at an angle of about 

 26° with the longer edge. Many of the cracks exhibit slight decom- 

 position, starting from them, and are sometimes occupied by calcite. 

 The pyroxene, under the microscope, hardly differs from the one 

 already described, except that the green tint is slightly richer and one 

 or two crystals contain the small dark brown negative crystals, com- 

 mon in hypersthene and diallage. The dominant cleavage, as before, is 

 along the clinopinacoid.* The thud mineral proves to be an altered 

 enstatite, but I leave the details for the present, as it is better pre- 

 served in another rock. A fourth constituent is also present, but more 

 sparingly, viz., a pale brown mica, only moderately pleochroic 

 (phlogophite 1). It occurs generally in plates, averaging about 0*1 inch 

 long. The minerals appear to have formed in the following order : 

 (a) garnet, (b) diopside, (c) mica, (d) enstatite. As before, iron oxides 

 are very inconspicuous ; there may be a grain or two (small) of ser- 

 pentinised olivine. The marked presence of enstatite distinguishes 

 this rock from the others, but it differs from the eulysites by the substi- 

 tution of that mineral for olivine, and so links those rocks to the more 

 ordinary eclogites. The occurrence of a little mica indicates the 

 presence of a small amount of an alkali in the magma. If necessary 

 we may name it newlandite, but personally I should prefer to call it an 

 enstatite-eclogite, for I think the coinage of fresh titles more often a 

 bane than a boon to science. 



5. This boulder is almost perfect, except that the general flatness of . 

 one side indicates either traces of an old fracture or considerable loss 

 by crumbling. The surface has been smooth, but it has suffered from 

 unequal weathering of the minerals. Its girth, in three directions at 

 right angles, is approximately 20 J in. by 19 J in. by 17 J in. It appears 

 only to differ from the last-described in having its garnets a shade more 

 purple, and in an approach to a banded structure ; the diopside being 

 rather more abundant in a middle zone, the garnet in one, the enstatite 

 in the other of the outer zones. Being satisfied that it is merely a 



* As noticed by Professor Lewis, ut supra, p. 22, in the diopside the prism 

 cleavage has practically disappeared, and a clinopinacoidal cleavage replaces the ^ 

 orthopinacoidal usual in diallage. 



