PROCEEDINGS OF SECTION C. 367 



The results obtained in many of these papers were summarised in 

 Hutton's descriptions and classification previously noted. His work is 

 certainly the most important in this as in many other fields of geological 

 inquiry. 



For the purposes of this paper it is deemed to be sufficient to give 

 a general account of the igneous rocks of each district, noting their 

 general characters only, and defining, as far as the author's knowledge 

 will allow, the areas over which the various rocks are found. In order 

 to keep the geological bearings of the matter as prominent as possible, 

 the subject will not be developed in the manner that would be demanded 

 if the gradations of petrographical classification were the first con- 

 sideration. The areas of occurrence of igneous rocks will be taken in 

 order, and consideration of the rock types and of the period of intrusion 

 or of emission will be referred to in connection with each igneous area. 

 In following this method it will be found that very different rocks will 

 be mentioned in close connection, and, on the other hand, one and the 

 same type of rock will have to be mentioned in descriptions of several 

 different areas. 



In many instances there is at present no definite knowledge as to 

 the date of intrusion or of eruption of the rock districts that are to be 

 described. In all cases, however, there are certain data that can be 

 relied on for ascribing more or less definite limits to the period during 

 which the formation of the rock masses can have taken place. The 

 igneous areas will be taken in the probable order of their formation. 



It is generally agreed that the oldest mass of igneous rocks in New 

 Zealand is the great plutonic gneissic area of the sou.th-west coast of 

 Otago and the greater portion of Stewart's Island. Captain Hutton at 

 first referred the huge mass to the Archaean period (1875), but afterwards 

 regarded the rocks as representing the plutonic reservoir from which 

 volcanic rocks of much more recent date (Carboniferous) were derived. 

 Sir James Hector referred to the whole of this mass of rocks as belonging 

 to the gneiss-granite formation of South America of Hochstetter. I 

 believe that there is at present a tendency amongst New Zealand 

 geologists to regard the whole mass of the rocks as extremely ancient. 



The most frequent type of rock is a diorite gneiss. The hornblende 

 is extremely green, and much epidote is to be found in the felspar. 

 Magnetite is alw^ays present, and the green hornblende often includes 

 quartz in the manner described by Holland in the charnockites of South 

 India. 



Granites and true gneisses are not uncommon. At Golden Bay, 

 Stewart Island, the granite is grey, and has a vein of a very distinct 

 graphic granite, the felspar of which is microcline-microperthite. At 

 Rugged Point, Stewart Island, a large intrusive acidic mass stands 

 on the border line between a graphic granite and a granophyre. At 

 Deas Cove, Thompson Sound, a true gneiss occurs. 



Granulites are of frequent occurrence. Usually there is relatively 

 little quartz. Garnet is very abundant, and rutile is nearly always 

 present. A pale-green pyroxene often occurs with the garnet. Green 

 hornblende is frequent in some of the specimens. The granulites 



