Uttley. — Gtologij of the Neighbourhood of Kakanui. 19 



Art. II. — The Geology oj the Neighbourhood oj Kakanui. 



By G. H. Uttley, M.A., M.Sc. 



Communicated by Dr. J. Allan Thomson. 



[Bead before the Wellingtoji Philosophical Society, 27th October, 1915.] 



Introduction. 



Previous geological work in the Oaniaru coastal district has resulted in 

 somewhat discordant conclusions. McKay (1877) has assumed an uncon- 

 formity to exist between the Cretaceo-tertiary and Tertiary series, but he 

 relies on difierences of dip and on volcanic action as evidencing the exist- 

 ence of a land surface. It is pretty well agreed now, however, that the 

 greater part, if not all, of the volcanic rocks in the district were ejected 

 be leath the sea. Difierence of dip at widely separated points carries no 

 weight where the rocks have been folded and faulted as at Oaniaru Cape, 

 where McKay seeks to establish his unconformity. The supposed strati- 

 graphical break, therefore, between a Tertiary and a Cretaceo-tertiary 

 system does not exist, and there is no palaeontological ground for the 

 recognition of the latter system so far as the Oamaru district is con- 

 cerned. 



Hutton (1887) placed a break between the Oamaru limestone and the 

 overlying greensand in certain localities where a nodular band, described 

 in detail below, is found to occur — viz., at All Day Bay and Deborah — 

 but other observers except McKay have refused to recognize the uncon- 

 formity. Hutton did not rely on palaeontological evidence, and included 

 both the greensand and limestone in his Oamaru system, but inferred 

 an unconformity from the waterworn surface of the limestone and the 

 difierence of dip. The evidence will be discussed in detail below. 



Park (1905) introduced an altogether new interpretation of the suc- 

 cession when he stated that two limestones existed in the Oamaru district, 

 separated by the Hutchinson Quarry and Awamoa beds, the lower being 

 termed the Oamaru stone and the upper the Waitaki stone. It is certain 

 that the limestone of the Devil's Bridge, which he calls the Waitaki stone, 

 is not underlain, as he states, but overlain by glauconitic sandstone — the 

 Hutchinson Quarry beds. The rocks underlying the limestone may be seen 

 to the north at Brockman's Hill, and consist of tuff and a sill of dolerite 

 dipping beneath the limestone — that is to say, the limestone of the Devil's 

 Bridge has the usual stratigraphical position of the Ototara limestone, 

 forming the middle member of the Oamaru system. It is only in the 

 neighbourhood of Kakanui that Park shows the two limestones in super- 

 position in the same section, and I shall endeavour to show beloM' that he 

 has misread the sequence. There are two limestones represented in the 

 same section on the south side of the Kakanui River, but they are separated 

 by volcanic rocks, and the upper limestone is followed by the Hutchinson 



