106 Miss M. C. Stopes—On Concretionary Noduiles. 
numerous little dodecahedra of sodalite, turbid in the interior, 
abundant green pyroxene and deep brown melanite, and some rather 
irregularly-shaped crystals of pale sphene. The pyroxene is an 
egirine-augite with strong pleochroism in bluer and yellower shades 
of green. ‘he extinction-angle in vertical sections scarcely exceeds 
a value of about 30°. In one clinopinacoidal section the main part of 
the crystal gives 32°, while a border of rather deeper colour gives 27°. 
The ground-mass of the rock, with well-pronounced flow-structure, is 
composed of sanidine, nepheline, and a pyroxene, apparently egirine, 
while slender needles of apatite are seen in places. 
The third type of phonolite [4715] differs from that last described 
in carrying hornblende. The sanidine, nepheline, sodalite, egirine- 
augite, and melanite are present as before, and the ground-mass is of 
nepheline, sanidine, and egirine, with fluxion-structure. The horn- 
blende crystals are idiomorphic, usually twinned, and in colour from 
brownish-green to greenish-brown in the thin slice. They have been 
corroded by magmatic resorption, the product of this reaction being 
green egirine-augite, which mineral also occurs separately in small 
idiomorphic crystals. It appears probable that the aggregates of 
egirine crystals noted in the first type [4710] have likewise been 
formed at the expense of hornblende, the transformation in that case 
being complete. It may further be enquired how far the seemingly 
independent crystals of pyroxene in these rocks may be due to the 
breaking-up of such aggregates, which originated as resorption- 
pseudomorphs after hornblende.! If there be any truth in this 
suggestion, Doelter’s distinction between augite -phonolites and 
hornblende-phonolites may perhaps mark no very essential difference. 
It is noteworthy that, in the phonolite from this neighbourhood which 
he studied, the two generations of pyroxene were found to differ 
greatly in composition, the one being an augite containing but little 
soda, and the other apparently an acmite or egirine with a remarkable 
content of manganese. 
The tephrites, basanites, felspar-basalts, and nepheline-basalts 
recorded by Doelter from various parts of the island of Santiago do not 
seem to be represented in the ‘“‘ Beagle”’ collection, so far as can be 
judged from megascopic characters; and the prevalent types in the 
district of Porto Praya are doubtless fairly illustrated by the specimens 
which we have selected for examination. 
IlJ.—Tue Revation oF tHE Concrerionary Noputrs oF THE YARRA 
To tHE CatcarEous NopuLes Known As ‘ Coat-Batts.’ 
By M. C. Srorzs, Ph.D., D.Sc., Lecturer at Manchester University. 
PHEROIDAL concretions from the Yarra estuary which were 
found to contain plant-remains were described by Mr. Chapman 
recently in this journal.* ‘The structures in themselves are of 
1A like question has been raised by Washington with reference to the augite- 
grains in many hornblende-andesites: Journ. Geol., vol. iv (1896), pp. 273-278. 
2 F. Chapman, ‘‘ On Concretionary Nodules with Plant-Remains tound in the Old 
‘Bed of the Yarra at S. Melbourne; and their Resemblance to the Calcareous 
Nodules known as ‘ Coal-Balls’”’? : Guoz. Mac., December, 1906, p. 553. 
