so 
A. B. Edwards. 
Ill [7230] tlio plagioi'laso latlis poaraer-grained, thoiigli still small, 
and dospitft partial kaoliiiisation, show extinction angles np to 12^ in the 
symmetrical zone, indicating that they consist of acid andesine (Ahyo). The 
amygdnles in this rock are tilletl (i) with chlorite ; or (ii) with quartz and 
unt^^ inned felspai’, stained with iron oxide, and sometimes accompanied by , 
chlorite ; or (iii) witli (piartz and chlorite. In other respects, however, the 
rock is identical with [7240]. 
The same texture is prt^served in [3759] from the Synnott Tableland, but 
in this rock the felspar is so altered to mica and kaolin material that its com- 
position camiot bo made out. In addition the rock, which contains numerous 
amygdulos of chlorite, is stained deeply with limonite. 
In the absence of a chemical analysis, these rocks might be regarded 
as basic andesites, but they have been classified as andesine-basalts in view of 
their general resemblance to the other rocks of the region, which when analysed 
prove to be baselts. 
5. Hornblende-oUgoclase-basalL 
[7248], from, the Hann River, near its junction with the Fitzroy River (analysed). 
This variety, which is represented by a single specimen from the south- 
eastern part of the area, is a micro -crystalline rock consisting of laths of 
plagioclase and idiomorphic micro-phenocrysts of pyroxene, set in a dark 
mesostasis of groundinass which has partially crystallized as radiating sheaves 
of a grey-bro\ni hornblende tluit shows almost straight extinction. The 
plagioclase is largely altered to secondar\' mica, hut lamellar tvdnning can be 
made out in some t-rystals, and gives extinctioir angles up to 10*^ in the sym- 
metrical zone, so that the felspar apjjears to bo basic oligoclase of a composition 
Abyo-Abyr^. T'ho |)yroxene i^ completely altered to chlorite, so that its com- 
position (Uinuot be determined. In places it is ophitic towai'ds the ];)lagioclase. 
The hornhleinle fibres are sometimes interleavetl w ith green chloritic material, 
representing original glass, anil less frequently with line felspar laths. In view 
of the acid nature of the plagioclase, and the abundant hornblenile, the rock 
resembles an andesite, hut a chemical analysis (Table 11, Xo. 4) indicates that 
it is a basalt. The fine texture of the rock is shown in Plate 2, Fig. 4. 
6. Volcaniv Tuff. 
[37or>], from the Synnott Tableland, north-east of Camp F.B. 32. 
This specimen is from a much weathered rock consisting of angular 
fragments, up to 1 cm, across, of highly chloritized material which contains 
a few small latlis of altered felspar, cemented together by material consisting 
chiefly of limonite, chlorite, and fine mosaics of secondary (juartz. The rock 
is almost certainly a w'eathered tuff. 
DISCUSSlOX, 
Tlie oufcro]5s of basaltic rocks iu the North Ivimherley region cover an area 
estimated by Easton (1922) as about (>,250 square miles. The inadequacy 
of any generalisations concerning these rocks, based on an examination of 
a collection of only 35 specimens is manifest. However, the s{)ecimens dis- 
play a marked uniformity in their general petrological character, wdiieh, 
coupled with the wide scatter of the localities from which they were obtained, 
justifies some suggestion as to the probable petrological character of the 
North Kimberley basalts as a whole With the excei>tion of [3771] (Table 1 
