598 MESSRS. S. H. REYNOLDS AND C. I. GARDINER [Nov. 1 896, 



without any other secondary material having heen developed. The 

 iron ore is dichroic, being red-brown and purple-brown in colour ; in 

 polarized light it assumes a rather brighter red-brown colour, the 

 greatest amount of absorption taking place when the cleavage-lines 

 are parallel to the short axis of the polarizer. Cracks sometimes 

 run through the outer coat of secondary material which are filled 

 with an iron ore distinctly redder than the above-mentioned one, 

 and this is probably haematite. The edge of the core, where it 

 comes in contact with the outer ring of secondary material, is very 

 ragged and uneven. In some cases the purplish iron ore occurs not 

 only as the core of the replaced augite, but also in the cracks and as 

 a rim fringing the whole crystal-outline, while in other cases it has 

 come in irregularly. In a few instances the iron ore occurs in relation 

 to little patches of serpentine, which probably represent original 

 crystals of olivine. 



Another mineral sometimes present, though found more frequently 

 in the rocks of the Hill of Allen, occurs in the form of small brown 

 or yellow rounded grains with a radiating structure. They can 

 often be completely rotated under crossed nicols without extin- 

 guishing. They are found most commonly enclosed in amygdules 

 of chlorite, and are probably cbalybite. 



Some of these basalts possess large platy felspars and serve as a 

 link to a peculiarly coarse basalt which is found at the western end of 

 the hill. This is a very striking rock ; its junction with the basalts 

 beneath is uneven, and portions of the underlying rock appear to 

 have been enclosed in its base. A hand-specimen shows a grey 

 compact groundmass, in which are numerous greenish felspars often 

 almost circular in section, sometimes | inch in diameter, and -jig- inch 

 thick. There is a general tendency for these felspars to be arranged 

 with their flat faces parallel to each other. 



A section of this rock shows a groundmass of lath-shaped felspars, 

 augite, and magnetite. The augite is very much more plentiful in 

 this groundmass than in that of any other rock from the hill ; it is 

 allotriomorphic, filling up the spaces between the felspar-needles, 

 which are not often twinned and give small extinction-angles, being 

 apparently allied to oligoclase. Some serpentine and small crystals 

 of a yellowish pseudomorph after rhombic pyroxene are also 

 present. The porphyritic constituents are, firstly, large plagioclase- 

 felspars allied to labradorite and often much altered, and secondly, 

 groups of augite-crystals, the individuals of which are frequently 

 well zoned. Amygdules are fairly plentiful ; their outermost rim is 

 generally formed of partially spherulitic quartz, within which is a 

 mass of green chloritic mineral, often enclosing numerous small 

 circular spaces filled with clear transparent quartz, which is some- 

 times beautifully spherulitic. 



Though this rock has been found only towards the western part 

 of the hill, and its base is irregular and sometimes encloses portions 

 of the underlying rock, there seems no necessity to consider it 

 intrusive. The adjacent rocks show no sign of alteration, and there 



