684 Transactions. — Geology. 



rise in the line representing its major axis. Hochstetter, in 

 his geological map of the Auckland Province, shows the dis- 

 tribution of trachytic lavas to the west and north of Taupe 

 Lake, but he appears to have thought that the lavas which 

 surround Tauhara Mountain did not extend for any distance 

 to the east or north-east ; and it is very certain that he had no 

 idea that volcanic rocks were to be found of any extent to the 

 east and north-east, or that they struck through the island in 

 the direction of Hicks Bay. 



Hochstetter's opinion as to the sequence of volcanic 

 phenomena is very suggestive. He says, " The iirst volcanic 

 eruptions were submarine, consisting of vast quantities of 

 trachytic lava, breccia, tuff, obsidian, and pumice-stone, which, 

 flowing over the sea, formed an extensive submarine volcanic 

 plateau. The volcanic action continuing, the whole mass was 

 upheaved above the level of the sea, and new phenomena 

 were developed. The eruptions going on in the air instead of 

 under the sea, lofty cones of trachytic and phonolitic lava, of 

 ashes, and cinders were gradually formed. These eruptions 

 breaking through the original submarine layers of trachytic 

 lava, breccia, and tuff, raised them, and left them as we now 

 find them, forming a more or less regular belt round the 

 central cones, and having a shght inclination from the centre 

 outwards." 



This theory assumes three periods of volcanic activity — 

 First, submarine, with deposition of trachytic lavas ; second, 

 elevatory, when the whole of the submarine deposits were 

 raised above sea-level ; third, formation of cones. Unfortu- 

 nately, Hochstetter does not suggest a time when the volcanic 

 phenomena began, or what sedimentary rocks were contem- 

 porary with the elevation of volcanic ones. But the three 

 periods agree well with the distribution of pumice through the 

 rocks of this district. 



In volume xx. of the Transactions, Article xxxix., there 

 is a paper on "The Geological Distribution of Pumice along 

 the East Coast," and three separate periods of deposition are 

 shown to have taken place: 1st, a Miocene (?), Cretaceo-Ter- 

 tiary of the Geological Survey ; 2nd, a Pliocene ; 3rd, a Eecent. 

 If the distribution of the pumice over the Island agrees with 

 periods of activity, as stated by Hochstetter, then the Mio- 

 cene (?) period was one when the North Island presented a 

 few islands only in place of its present area. It was towards 

 its close that the trachytic lava-flows welled up, as it were, 

 without the formation of cones and spread themselves, as they 

 have done, in such a curious manner over the whole of the vol- 

 canic belt. During the Pliocene period the North Island had 

 grown considerably, and the pumice, with much of the debris, 

 was spread over the district both east, north, and south by the 



