Vol. 62.] GEOLOGY OF DUXEDItf (NEW ZEALAXd). 411 



They are evidently both rather basic types of rock ; but there 

 does not appear to be any indication in the analyses of the cause 

 that has made them, during their solidification, assume states of 

 crystallization so very different. 



In one outcrop on the shore of Papanui Inlet, large fragments of 

 quartz are contained in abundance in the Papanui Dolerite. They 

 are of all sizes, up to 6 centimetres in diameter. Their structure 

 shows that they are derived from schist that has been broken off 

 during the ascent of magma through it. In slices, the margin of 

 the quartz is seen to have a dense felt of augite-crystals, with their 

 longer axes at right angles to the margin. 



(A) The Mount-Charles type forms extremely -large lava- 

 flows at the centre and east of Otago Peninsula. One of these 

 is well- exposed at the Xatural Bridge, Sandy Mount, where it is 

 300 feet thick and has a well-marked, coarse, columnar structure. 

 Almost the whole of the Mount- Charles Peninsula is composed of it. 

 Except for two small patches at Whare Flat and Blanket Bay, it 

 has not been found to the north or west of Otago Harbour. At 

 the Natural Bridge, it rests upon a thick breccia of basic rock. 

 Near Portobello, it is much invaded by trachyte. A dyke of it 

 penetrates a basic breccia at the southern head of Hooper's Inlet. 

 At the north side of Hooper's Inlet there is apparently an intrusion 

 of trachyte into it, and a dolerite of the Papanui t5*pe either 

 intrudes into it or underlies it. 



It appears, therefore, that this rock is one of the oldest of the 

 whole series ; for it is, in the Portobello area, older than the 

 trachyte, itself the lowest of the rocks in this area, which is the 

 centre of the whole volcanic district. 



(B) The Papanui type is the most widespread of all the rocks 

 of the area. At Sea View, it lies directly upon the calcareous 

 sandstone. By Otago Harbour, opposite Logan's Point, it occurs 

 below the trachytoid phonolite. At the See House, it is below 

 the andesite and the trachytoid phonolite. It appears to have been 

 the product of one of the older eruptions, and apparently ceased 

 before the emission of any trachytoid phonolite. 



This rock — or at any rate a type indistinguishable from it by 

 microscopic methods — occurs over a wide area in Otago ; for it is 

 found at "Waifiata in Central Otago and at Puketapu near Palmerston 

 North, and a very similar rock occurs at Banks Peninsula. The 

 specimens obtained at Papanui Inlet are coarser than any that are 

 found elsewhere. 



17. Basalt. — There is a great variety of basalts in the Dunedin 

 area. They vary from comparatively-acid types, to others that are 

 almost limburgites. 



At High Cliff, a basalt occurs, with very little olivine and a fine- 

 grained groundmass of pale augite and felspar-microliths, giving 

 to the rock a pilotaxitic structure. At Sea View, the olivine-grains 

 are very large and conspicuous, the augites of moderate size, and 



