VOLCANIC ACTIVITY IN SOUTHERN QUEENSLAND. 123 
the south. <A shght change in sea-level resulted in the 
deposition of freshwater sediments (equivalent to the Greta 
Measures). Following this the area seems to have been 
subjected to a series of oscillatory movements, with the 
result that while the major portion of the sediments 
deposited are marine in nature (though of very shallow 
water tvpes), there are intercalated with them at least two 
bands of freshwater deposits. The net result of these 
oscillations was a gradual change from marine conditions 
to terrestrial conditions, and it was during this change that 
the voleanic activity which is the subject of this paper was 
manifested ; for while a considerable proportion of the lavas 
and tuffs are found associated with fossiliferous marine 
strata, the major portion of them shows evidence of having 
been poured out on a land surface. No further marine 
deposits have been laid down in the area from this time to 
the present day. 
At some time subsequent to the deposition of the Upper 
Marine sediments and the associated volcanics, and ante- 
cedent to the deposition of the Ipswich Series (of Upper 
Triassic age), there were intruded the huge well-known 
granitic masses of New England and Southern Queensland. 
The representative of this group in the Silverwood area is 
the coarse acid Stanthorpe granite. This might, perhaps, 
be expected to show some evidence of relationship with the 
voleanics, but a comparison of chemical analyses shows 
important points of difference, for whereas the alkalies of 
the Stanthorpe granite are approximately equal, there is in 
the voleanic rocks a normal soda value which predominates 
over an abnormally low value for potash. 
If we go a little further afield, however, we meet, at 
Greymare and elsewhere, with granitic rocks of a somewhat 
earlier phase than the acid Stanthorpe granite, which must 
therefore approximate even more closely in age the Permo- 
Carboniferous voleanics. One of us has endeavoured!! to 
show that the late Palwozoic granitie rocks of Southern 
Queensland can be divided into an earlier ‘‘Grey Phase,’’ 
characterised chemically by a marked predominance of soda 
over potash, and a later *‘ Pink Phase,’’ where the alkalies 
are approximately equal or have potash in excess of soda. 
11 Bryan, W. H., Proc. Roy. Soe. Qid., 1922, p. 148. 
