124 G. D. OSBORNE. 



calcite, serpentine and quartz in association. In many 

 cases carbonates have probably replaced original hydrous 

 magnesium silicate pseudomorphs after olivine. 



The base of the rock presents some unique characteristics. 

 Magnetite is abundant and exists as idiomorphic and sub- 

 idiomorphic octahedra and also as minute needles. The 

 latter are often arranged in radiating groups or in parallel 

 lines. Many of the needles stand perpendicular to the 

 phenocrysts, which were evidently floating about in the 

 magma just prior to complete freezing. At other times 

 the magnetite grains have wrapped round the phenocrysts 

 in coronal fashion. 



The rest of the base consists of small brown prismatic 

 augites of the second generation and of felspar laths. The 

 augites are fresh and free from iron inclusions. Some 

 grains are simply twinned. The felspar is altered to sericite 

 and chlorite. A careful search failed to reveal the presence 

 of felspathoids or of melilite. The rock is holocrystalline 

 and exhibits glomero-porphyritic structure in places. 



(b) Dyke No. 3. — This rock is considerably decomposed 

 and is evidently coarser in grainsize than the other dyke 

 rocks. The field presented in the microscope is 60% rhombo- 

 hedral carbonate, but careful examination reveals evidence 

 of the former presence of olivine, augite and felspar. There 

 is a distinct tendency to ophitic fabric. It is clear that 

 the rock was originally an olivine dolerite or olivine basalt. 



(c) Dyke No. 1. — This is the most important of the three 

 dykes, in that it is the matrix of the interesting xenoliths. 

 In hand specimen it has a slaggy appearance and is char- 

 acterised by a large number of small joints. 



The dyke rock, a basalt, varies mineralogically from 

 point to point. Whether this difference has been contributed 

 to by assimulation of xenolithic material or not, is hard to 



