370 PROCEEDINGS OF SECTION C. 



Granites and granophyres, with various types of volcanic rocks, 

 are abundant as pebbles in conglomerates of Maitai (Carboniferous) 

 and Triassic age throughout the colony, from the North Cape to 

 Waipapapa Point. In almost every instance it has so far been found 

 impossible to trace them to their origin. 



So far as known, dyke rocks are relatively uncommon throughout 

 the country, and true sills are almost unknown. Exceptions to this 

 statement are to be found in many of the volcanic districts, notably 

 Dunedin ; but they will be described when the volcanic areas are dealt 

 with. 



There is a well-defined system of dyke rocks of the camptonite- 

 monchiquite series, which extends along the Southern Alps from the 

 Taramakau to the Shotover. Dr. Bell has mentioned several of these 

 at the camptonitic end of the series in his bulletin of the Hokitika 

 quadrangle recently issued. In that area the dykes penetrate granitic 

 rocks. Mr. J. P. Smith has sent me specimens of similar dykes pene- 

 trating granite near Lake Brunner, as well as a vogesite from gravels 

 in the same locality, I have obtained similar rocks near the Big 

 Wanganui, further south, and from the Shotover gravels specimens of 

 true monchiquite can be obtained in quantity ; but I have found none 

 further south, though to the east they extend some distance down the 

 Kawarau Valley, according to Professor Park. Except that the date of 

 intrusion of these rocks is subsequent to the age of the granite, there 

 is no information as to their age. 



There is a porphyrite dyke at the Nuggets, and numerous diabase 

 dykes at Reefton and at Mo3raki, and dykes of quartz porphyry at 

 Brunner. 



In the South Island there is at Nelson and at Orepuke, as well as 

 several intermediate places, a well-defined lava of Maitai age. In hand 

 specimens the rock is green, and in thin section the coloring is 

 found to be due to chloritic and serpentinous matter evolved during the 

 changes that the rocks have undergone. The felspar is much decom- 

 posed, and is apparently labradorite. Augite (idiomorphic) is abundant 

 in large crystals of a very pale yellow color and pseudomorphs of ser- 

 pentine after olivine. The rock is often vesicular. The substantial 

 identity of this rock throughout the South Island causes me to class 

 it everywhere as a melaphyre, though in two different exposures Hutton 

 classed it as leucophyre and diabase, and Sir J. Hector and his officers 

 called it aphanite. 



Later volcanic rocks occur in the Clent Hills and further north. 

 The largest development is in the Mount Somers area ; but there is a 

 nearly continuous outcrop from the Waimakariri to the Rangitata. 

 The most characteristic rock is a white rhyolite, with abundant quartz 

 and usually a good deal of almandine. Glassy varieties are also com- 

 mon, and typical pitchstones are frequent. No spherulitic structure or 

 development of crystallites other than globulites occur, and the glass is 

 therefore particularly transparent. A wliite rhyolite, similar to the 

 one mentioned above, occurs also at the head of Lyttelton Harbor. 



