NODULES IN TIIE BASALTS. 
107 
Some of them are of the usual type common to many basalts, and consist mainly 
of olivine and enstatite, with brilliant green chrome-diopside, like the nodules in the 
limburgite of Franklin Island.* 
Others, however, differ from most of those previously described in consisting to a 
large extent of plagioclastic felspar, and thus have the character of gabbros rather than 
of peridotites.f 
Such gabbro-like nodules were found in the hornblende-basalt (385) from the 
Sulphur Cones, and in the limburgites from the neighbourhood of Winter Quarters 
(408, 316, 335, 415), as well as in the basalt (375) from Harbour Heights to which 
reference has been made in the Report on the Field-geology (p. 13). 
In the latter rock many of the inclusions, as stated by Mr. Ferrar, are quite 
angular. In fact, some of them appear to be only loosely held in the basalt, like 
fragments caught up in the molten mass. In most of the other specimens, however, 
the nodules present the more usual rounded appearance, and are completely 
enclosed by the basalt. In some cases (385) the junction is perfectly sharp, and the 
rock shows under the microscope no variations in structure or composition in the 
neighbourhood of the nodule. In other cases (335) the basalt has obviously permeated 
the nodule in thin veins. This nodule (335) is composed mainly of pale-green augite, 
enstatite and olivine, but contains also a little basaltic hornblende and biotite, and 
some plagioclastic felspar in broad plates. Where the basalt has permeated the nodule, 
the augite-plates have been converted into aggregates of small grains which bear some 
resemblance to the bronzite-chondrules in meteorites. The hornblende in the nodule 
may possibly have been derived from the basalt, which contains phenocrysts of similar 
hornblende ; the biotite also may have resulted from the interaction of basalt and 
nodule ; but the felspar can hardly be conceived to owe its origin to the basalt, since 
the latter is of distinctly limburgite-type, showing under the microscope little or no 
felspar. Moreover, the most felspathic nodules of those examined, viz., 385 and 316, 
show no signs of having been attacked by the enclosing basalt. 
These two felspathic nodules consist of granular aggregates of plates of labradorite, 
giving symmetrical extinctions of 20°-30°, and irregular crystals and corroded patches 
of nearly colourless augite having a roughly parallel arrangement ; a little olivine is 
alsQ present in specimen 385. Under the microscope the pale yellowish-brown augite 
has a rough, dirty appearance due to numerous inclusions. These consist for the most 
part of gas-bubbles, glass and opacite, but some fantastically-shaped ones are probably 
liquid inclusions. One crystal showed long black needles arranged in parallel lines, 
like those observed by Dannenberg in augite-nodules in the basalts of the Rhine. | 
The felspars in these nodules also enclose numerous gas-bubbles. 
* Prior, Kep. ‘ Southern Cross ’ Collections (British Museum), 1902, p. 328. 
t Felspathic nodules in the basalts of the Siebengebirge have been described, see Dannenberg, Tschermak’s 
Min. Petr. Mitth., 1895, Bd. xiv, p. 35; Laspeyres. Verh. naturh. Ver. pr. Bheinl., 1900, Jahrg. lvii, p. 194; and 
Zirkel, Abhand. math.-phys. Cl. d. konigl. sachs, Ges. d. Wiss,, 1903, Bd. xxviii, p. 165. 
% Dannenberg, l.c. p. 40, 
p 2 
