106 Transaction*. 



Art. VII. — The Volcanic Rocks of Oamaru, ivith Special Reference to 

 tlicir Position* in the Stratigraphical Series. 



By G. H. Uttley, M.A., M.Sc, F.G.S., Principal, Scots College, Wellington. 



[Read before the Wellington Philosophical Society, 16th July, 1016 ; received t>y Editors, 

 31st Deceinber, 1917; issued separately, 24th May, IH18.] 



Contents. 



I. Introduction. 

 II. Succession of the Rocks of the Oamaru Series. 



III. Previous Opinions in regard to the Horizon of the Volcanic Rocks. 



IV. Effects of these Opinions on the Classification of the Oamaru Series. 

 V. Descriptions of the Sections. 



(1.) Oamaru Lighthouse. 

 (2.) Oamaru Rifle Butts. 



(3.) Hutchinson Quarry and Neighbourhood. 

 VI. The Pillowdavas. 

 VII. Chemical and Petrographical Notes. 

 VIII. Conclusion. 



I. Introduction. 



Interpretations of the geology of the Oamaru coastal district where the 

 typical Oamaru series is developed have varied greatly in the past, and, 

 although there is now pretty general agreement as to the broad features 

 of the rock-sequence, it is essential that more detailed stratigraphical work 

 should be attempted if the best results are to be obtained from the deter- 

 minations of the Tertiary fossil Mollusca and Brachiopoda, which are being 

 carried out by Mr. H. Suter and Dr. J. Allan Thomson. Many of these 

 fossils have been collected from the Oamaru district, the exact locality 

 and rock from which they have been gathered are known, and, if the strati- 

 graphical sequence can be determined in greater detail than has been done 

 in the past, correlation of Tertiary rocks in other parts of the Dominion 

 with those developed in the typical locality will possess a sounder basis 

 than it does at present. 



Misinterpretations of the rock-sequence at Oamaru have undoubtedly 

 been caused by faulty identification of the horizons of the volcanic rocks, 

 and it will assist stratigraphical work if these can be determined more 

 accurately. 



The position of the lowest volcanic rocks, the Waiarekan, is not in ques- 

 tion ; it is generally agreed that they lie immediately below the Ototara 

 limestone, and my work in the North Otago district has convinced me 

 that they are invariably associated with deposits of diatomaceous earth 

 in the Oamaru and Papakaio areas. Difference of opinion has, however, 

 been sharply marked when dealing with the volcanic rocks near the Oamaru 

 coast. These have been correlated with the tuffs in the Waiareka area ; 

 important unconformities have been introduced into the sequence, on the 

 ground that the volcanic rocks are clear evidence of the existence of 

 a former land surface. An attempt will be made in the present paper to 

 define more clearly the place of the volcanic episodes in the late geological 

 history of the Oamaru district. In 1916 I gave a detailed sequence of the 

 rocks east of the Waiareka Valley, and some of the evidence on which the 

 succession was based was presented in that paper. It is now proposed to 

 bring additional evidence by describing several sections in the neighbourhood 



