300 GEOLOGY AND PETROLOGY OF THE GREAT SERPEXTIXE BELT OF X.S.W; 



bringing up the Burimli beds beneath the cover of black soil. The width of the 

 range does not seem sufficient to permit of the development here of the full thiefe- 

 ness of the Kuttung Series (see Text-fig. 2). 



General Bemarks Concerning the Kuttung Series. 



Summarising the above facts we find that the Kuttung Series in this region 

 is made up of the following members: — ■ 



Upper Portion: Approximate Thickness. 



Tuft's and conglomerates 1600 feet . 



Bhacopteris tuffs and varve beds 50 



Upper Tillites, conglomerates and tuffs 1500 



Middle Portion : 



Khyolite Tuff 50 



Main Felspathic Grit 1000 



Lower Glacial Beds 1300 



Lower Portion: 



Felspathic tuffs and pebble beds (say) 4000 



Total 9500 



The total thickness of the Kuttung Series in this district is thus comparable 

 with the thickness of 7000 feet measured in the same series in the Paterson area 

 by Professor David and Mr. Sussmilch (4) . It would, however, be quite pre- 

 mature to attempt any detailed correlation. A striking point of distinction is the 

 comparative rarity of actual flows of volcanic rock in the Currabubula district, con- 

 trasted with their frequent occurrence in the Paterson region. 



Attention may here be directed to the writer's comment on the section exposed 

 on Rocky Creek near Bingara (2. p. 268), — "The series is, in ascending order; 

 Burindi tuft'aceous mudstoncs. followed by tuffs covered by a very gi'eat thickness 

 of coarse conglomerates with boulders of granite, porphyry and rhyolite in a tuff- 

 aceous groundmass, with interbedded layers of rhyolite and rhyolite tuff. Following 

 this there is more tuff, and al)ove a band, about fifty feet thick, of a hard cherty tuff, 

 very fine grained but including small pebliles of gi-anite, etc." [See also the 

 microscopic description (23, p. 720, M.B. 16).] "Following this is a mass of 

 coarse rhyolite tuff. Altogether the series cannot be less than two thousand feet 

 thick, and the hill at the side exposes at least five hundred feet more." 



The experience now gained leads the writer to conclude that this "hard 

 cherty tuff," observed by him in 1911, was also a glacial rock containing small 

 erratics, and that the section exposed on Rocky Creek is perhaps comparable \vith 

 the Middle and Lower Portions of the Kuttung Series as here described. 



As regards the conditions under which these sediments were deposited, it is 

 evident that the epoch of their foi'mation was one of continuous and energetic 

 explosive volcanic activity, accompanied by extensive glaciation. The apparent 

 absence of striated pavements and the rarity of the preservation of striae except 

 on the quartzite pebbles, together with the abundance of waterwom pebbles and 

 of "varve" rocks, seem to indicate that fluvio-glacial rather than purely glacial con- 

 ditions predominated, a conclusion whicli accords with that of Professor David and 

 ]\rr. Sussmilch (4) . At the same time, the unstratified beds containing large 

 boulders scattered through a felspathic matrix have soine features like those of 

 subglacial till. It must also be pointed out that the discrimination between glacial 



