Marshall. — Geology of North Island. 97 



basanites are usually fine-grained, though this character is far 

 less noticeable in the specimens from the Waikato area, which 

 are relatively coarse but even-grained, and thus different from 

 the Karioi-Pirongia rocks. 



A consideration of these statements will show that our know- 

 ledge at present allows us to classify the products of volcanic 

 action as follows : — 



1. Later Miocene, — 



(a.) Andesites of Cape Colville Peninsula. 

 (6.) Andesites of Manukau breccias in their many occur- 

 rences, 

 (c.) Rhyolites of north of Taupo. 

 (d.) Dolerites of Pirongia'and Karioi.* 

 (e.) Older basalts of Kerikeri.* 



2. Later Pliocene, — 



(a.) Hornblende-andesite of Mount Egmont. 

 (b.) Augite-hypersthene-andesite of Ruapehu and other 

 cones of the plateau. 



Hypersthene-dacite of Tauhara. 



Basanites of lower Waikato. 



(c 

 (d. 



3. Recent 

 (a. 

 (b. 

 (c. 



Andesites of Ngauruhoe and Tongariro. 



Basanites of Auckland and Bay of Islands. 



Andesite of Tarawera. 

 A very interesting type of basanite is found in the Domain 

 volcano, Auckland, in the form of ejected blocks only. The 

 iron-ore is ilmenite ; feldspar is oligoclase-andesine ; olivine in 

 elongated crystals ; augite is violet, and shows strong pleo- 

 chroism, and sometimes has a fringe of segerine ; nepheline 

 idiomorphic and small ; ophitic and micrographic structures 

 are well shown, the latter as typically as in the celebrated type 

 from the Labauer Berg. 



Summary. 



There is little evidence in regard to the structural meaning 

 of the direction of the North of Auckland Peninsula. 



That the plutonic rocks of Mangonui and Ahipara are diorites 

 and norites, but no evidence is available as to whether they 

 are intrusive or older than the Mesozoic sediments. 



Volcanic rocks are chiefly rhyolitic in the central region, 

 but the rhyolites are penetrated by andesitic pipes, over which 

 large cones have been built up. 



The lake-basins are probably areas of violent hydrothermal 

 explosions, and from these explosions pumice was distributed. 



* Perhaps early Pliocene. 

 4 — Trans. 



