BY O. E. WHITE AND W. A. MACLEOD. 79 



sections the tint deepens to a fine red. In the majority of 

 cases the Fayalites exhibit crystalline outlines, the pris- 

 matic form predominating, and giving excellent longitu- 

 dinal and cross sections. Here and there occur patches of 

 Fayalite exhibiting no discernable crystalline outline. In 

 length the crystals vary from ()-5 m.m. downwards. The 

 inclusions visible under a high power (one-sixth inch) 

 appear to be apatite and needles of felspar, and perhaps 

 glass, though, on account of their minute dimensions, it is 

 difficult to obtain good extinctions under crossed nicols. 



Under crossed nicols the Fayalites exhibit the ordinary 

 interference colours and the normal extinction of rhombic 

 crystals. Pleochroism is not noticeable. 



We have noticed neither augite nor olivine in any of the 

 sections examined, and most probably these are entirely 

 absent in this rock. Apatite was mentioned above as 

 occurring in the Fayalites. It is also found here and there 

 in the base as long needles of a faint violet-brown tint, 

 and exhibiting pleochroism from a very faint brotvn tint 

 to a deeper violet-brown (E > 0). On treating a section 

 with hydi-ochloric acid the apatites slowly dissolved out, 

 leaving the glass slip visible underneath. The Fayalites 

 were also attacked, though less rapidly. 



The base consists of a ground- work of glass, penetrated 

 with needles and fine laths of felspar running in all 

 directions, the whole being thickly dusted with grains 

 of magnetite. The felspars exhibit extinction angles, 

 varying from 40° to 48°, which, according to Michel 

 Levy's table for microlites, indicates a basic felspar, pro- 

 bably labradorite or anorthite. The percentage of lime 

 (7 • 34°/q CaO) in the analysis, and also that of the alkalies, 

 some 9° Q, point to the felspar being labradorite (in which 

 the proportion of alkalies to lime is approximately one to 

 three) mixed with a little andesine or some more acid 

 felspar. This supposition is based on the assumption that 

 the base is of the same composition as the microlites 

 of felspar, — a somewhat doubtful hypothesis. 



This rock appears to have followed the normal order 

 of consolidation, — the apatite and magnetite consolidating 

 first, then the Fayalite and felspars. It is difficult to 

 determine exactly the relation of the Faj^alite to the 

 felspar microlite, for, included in the Fayalite crystals, 

 appear thin rods, which in some cases are glass, but in 

 others are doubtful, on account of the difficulty of obtain- 

 ing good extinctions under crossed nicols. All the 

 jnicroscopic characteristics point to the conclusion that it 



