Formula.—Hypersth.-aug., matr., orth.
Remarks.—The same classification is to be employed here as in the case of the two previous orders, but as the rocks in my collection that belong to this order are not numerous (nine sections), it will be sufficient to refer to the general remarks on the order on p. [290].
Fourth Order of the Hypersthene-Augite Andesites.
Characters.—Groundmass presenting a rudely granular
appearance or blurred mosaic (microfelsitic).
Formula.—Hypersth.-aug., matr., fels.
Remarks.—My sliced specimens (five) are too few for the elaboration of this order to which the classification employed for the other orders is scarcely applicable. This is due to the partial decomposition or imperfect development of the pyroxene of the groundmass. The general characters of the order are given on p. [291].
The Plutonic Rocks.
These rocks are very infrequent and are for the most part hypersthene-gabbros or norites, with a few representatives of diorites[[110]] without pyroxene. True plutonic rocks did not come under my observation in the western half of the island (west of Lambasa and Savu-savu), those of Mount Thoka-singa in the Ndrandramea district making the nearest approach (see p. [302]). The localities in which they were found are below enumerated:—
| No. | Nature of rock. | Locality. | Mode of occurrence. | Page. |
|---|---|---|---|---|
| 1 | Hypersthene-gabbro | Avuka Range between Lambasa and Mbuthai-sau | Probably forms the axis of the range. | [180] |
| 2 | Ditto | Nawi, at the head of the Vui-na-savu River | Deep-seated. | [211] |
| 3 | Ditto | Valanga Range between Savu-savu and Natewa Bays | Probably forms the axis of the range. | [182] |
| 4 | Ditto | Ridge at the head of Na Kula valley between Savu-savu and Natewa Bays. | Ditto. | [184] |
| 5 | Hornblende-gabbro. | Ditto | Ditto. | [184] |
| 6 | Diorite | Vunimbua River, on south side of the Mariko Range | Loose blocks in river-bed. | [182] |
| 7 | Ditto | Coast cliffs west of the Salt Lake Passage | Large block in agglomerate-tuff. | [193] |