424 Transactions. — Geology. 



The basalt is fine in texture. Under the microscope it is 

 seen to consist principally of plagioclase, augite, and olivine. 

 The base is bluish-grey in colour, but not abundant. It is 

 crowded with microlites of feldspar and augite, and thickly 

 dusted with grains of magnetite. The feldspars occur as long 

 narrow laths. The phenocrysts show orientation in one 

 genei'al du-ection, which doubtless indicates the original plane 

 of fluxion. A little sanidine and apatite are present. 



The existence of this outlier of basalt proves that the 

 sculpturing of the present contours has taken place since the 

 close of the Pliocene— that is, after volcanic activity had 

 ceased in this part of Otago. 



Genekal Conclusions. 



The Tertiary marine sandstones, leaf-bed series, and over- 

 lying flow of basalt are exposed in vertical section in a face of 

 steep escarpment nearly 200 yards long and 400 ft. high. 

 The face is bare or covered only with a scanty vegetation, 

 thereby enabling the actual junction of the different forma- 

 tions to be examined at many points of contact. 



The geological relations are so clear that the Waikouaiti 

 section thus becomes of almost classic value when considered 

 in connection with the sequence of events that constitute the 

 geological history of the neighbourhood of Dunedin and the 

 region round about Mount Cargill and Waitati. 



Unconformity of Dunedin Volcanic Bocks to Oamarii Series. 

 — Within the watershed of the Waitaii, Silverstream, and 

 Kaikorai Streams the great pile of volcanic ejecta wliich forms 

 the hills around l^unedin is found resting upon different mem- 

 bers of the Oamaru series, of which the Waikouaiti sandstone 

 forms a part. 



An examination of the geological structure of tlie neigh- 

 bourhood of Dunedin shows that the Caversham sandstone 

 had been elevated and in some places highly denuded before 

 the commencement of volcanic activity in that region. The 

 unconformity between the marine series and volcanic rocks 

 is so well marked as to indicate a considerable lapse of time 

 between the formation of the one and the eruption of the 

 other. 



Unconformahle lielations of Leaf-bed Series to Oamaru 

 Series. — No one seems to doubt that the Waikouaiti sand- 

 stone is the horizontal equivalent of the Caversham sand- 

 stone. When, tlierefore, we find terrestrial beds composed of 

 material derived from volcanic rocks that lie unconformably 

 ujjon the Caversham sandstone near Dunedin resting upon 

 equivalent marine beds at Waikouaiti, we can only conclude 

 that even a greater unconformity in time exists between the 

 terrestrial beds and marine series at Waikouaiti than between 



