Tol. 62.] THE GEOLOGY OF DTJNEDIN (NEW ZEALAND). 381 



15. The Geology of Dunedin (New Zealand). By Patrick 

 Marshall, M.A., D.Sc, E.Gr.S., Professor of Geology in the 

 School of Mines of the University of Otago. (Read May 10th, 

 1905.) 



[Plates XXXVI-XXXIX.] 



Contents. 



Page 

 I. Introduction, and Description of the Topography of 



the Area 381 



II. Description of the Rock-Types, and their Geological 



Occurrence 387 



III. Chemical Classification 414 



IV. Origin of the Different Kinds of Rocks 416 



V. Summary 422 



I. Introduction, and Description oe the Topography 

 oe the Area. 



The eastern coast of the South Island of New Zealand has two 

 projecting points consisting of volcanic rocks of Kainozoic age. 

 These igneous masses constitute Banks Peninsula and the Otago 

 Peninsula. Except in regard to their physiographical nature, neither 

 of these areas has been submitted to accurate geological exami- 

 nation, although enough work has been done to show that both of 

 them offer a most interesting field for petrographical study. 



The general structure of Banks Peninsula was studied by Sir 

 Julius von Haast, 1 who traced and described various crater- walls 

 which were the boundaries of the foci of most intense volcanic 

 activity. The structure of one of these — Lyttelton Harbour — was 

 displayed with great clearness in the walls of the rail way- tunnel that 

 pierced it, and Sir Julius has given an accurate description of this. 



Many of the rock-specimens collected during the tunnel-driving 

 were described and figured by the officers of the Trench Campbell- 

 Island Expedition. Other rock-specimens from the district have 

 been described by Marshall, 2 Speight, 3 and Ulrich. 4 



So far as its general structure is concerned, Otago Peninsula 

 has received less notice, though brief descriptions have been given 

 by Hutton, 5 Hector, and Ulrich. 6 More detailed work has been 

 devoted to the Otago-Peninsula rocks, and some types were described 

 by Hutton, and later, in a far more elaborate manner, by Ulrich. 

 who was the first to recognize the specially-interesting series of 

 alkaline rocks that occurs here. 



i ' Geology of Canterbury & Westland ' 1875. 



2 ' Tridymite-trachyte of Lyttelton ' Trans. N. Z. Inst. vol. xxvi (1893) p. 368. 



3 * On a Doleritic Dyke at Dyers Pass ' Ibid. p. 408. 



4 'On the Occurrence of Nepheline-bearing Rocks in New Zealand' Rep. 

 Austral. Assoc. Adv. Sci. vol. iii (1891) p. 127. 



5 ' Geology of Otago ' 8vo. Dunedin, 1875. 



6 Rep. Austral. Assoc. Adv. Sci. vol. iii (1891). 



-Q.J.GkS. No, 247. 2d 



