96 Transactions. 



In the present state of our knowledge one appears justified 

 in making the statement that nearly all the cones that rise 

 above the rhyolite plateau are formed of hypersthene-augite- 

 andesites. Tauhara appears to be the only exception re- 

 corded. 



It may here be stated that Hochstetter referred to many of 

 these rocks as trachydolerites, and that this name has been 

 widely adopted in the reports of the Geological Survey of the 

 past. 



Hypersthene-andesites have a considerable development 

 further north. All the specimens that I have gathered from 

 the Waitakerei region belong to this type, and from the Little 

 Barrier Island a pure hypersthene-andesite was given me by 

 Mr. Cheeseman, F.L.S. At Whangarei Heads, Parua Bay, a 

 similar rock was found. At Whangaroa hypersthene-andesites 

 and hornblende - hypersthene - andesites were obtained from 

 St. Paul's Dome. One is probably justified in assuming that 

 these rocks occur in the other regions where the typical Manukau 

 breccia occurs — viz., at Hokianga and at the North Cape. 



In the central region it can be clearly seen that distribution 

 of pumice succeeded earlier eruptions of the Ruapehu region, 

 for at Waiouru and in the Onetapu Plains pumice rests on the 

 surface of andesitic rocks. That the distribution of pumice was 

 succeeded by eruption of andesitic matter is shown by the 

 andesite tuff that rests on the pumice in the same localities. 



Basaltic rocks show less variation, and have a wider occur- 

 rence. Pirongia and Karioi appear, from the specimens that 

 I have collected, to be formed entirely of a porphvritic rock 

 of this class, which is perhaps best called a dolerite. The olivine 

 is much serpentinised, augite in large crystals is plentiful, and 

 andesine-labradorite feldspar as well. The groundmass is augite 

 feldspar and magnetite. Amongst New Zealand rocks this 

 type resembles some of the dolerites of Dunedin more closely 

 than any others that I have seen. 



The older basalts which occur north of Kerikeri, and between 

 Kaitaia and Ahipara, are very fine-grained ; olivine much 

 serpentinised, and fine ; feldspar very plentiful, as well as augite 

 and magnetite. I do not know the localities from which the 

 eruption of these took place. 



The rocks of the cones at Auckland and of the Waikato 

 plateau, as well as those of the Bay of Islands, have always 

 been classed as basalts. All that I have examined prove to be 

 basanites. The nepheline is not present in any quantity, but it 

 can be detected by gelatinisation and Btaining, as well as by the 

 cubes of salt obtained when the solution derived from treatment 

 of the rock-powder with hydrochloric acid is evaporated. These 



