376 Transactions. — Geology. 



suggested that probably an older diatomaceous deposit had 

 been denuded for supply of the lower part of that undei- 

 description, and in which only fossil forms are found, while 

 the higher and last formed were manifestly due to diatoms 

 (of recent forms only) which had lived aud died within the 

 area wherein their remains had acciunulated. But this is not 

 the only explanation that may be advanced, and, this not dis- 

 posing of all the objections to it, before advancing any of my 

 own I deem it necessary to describe more closely the posi- 

 tion of the deposit and the conditions under which it has 

 accumulated. 



Between the valley of the Kawakawa Eiver (which from 

 Pakaraka lies to the east and south) and the fall westward 

 into the Hokianga Eiver the drainage is carried by the Wai- 

 tangi Eiver into the Bay of Islands. Between Waimate and 

 Ohaeawai on the west, to the hills south-east and east of 

 Pakaraka, and thence east and north to Black Bridge, the 

 upper Waitangi basin approaches to a circular form, and, 

 with the exception of the volcanic cones within it, may be 

 described as a depression surrounded by hills on all sides. 

 Before the outbreak of the late Tertiary volcanoes, Cretaceo- 

 tertiary beds covered most of the area from Turntable Hill to 

 "Waimate and from Black Bridge to the southern w'atershed. 

 Probably the earliest eruptions began in late Pliocene times ; 

 but, although at different places the volcanic forces must have 

 been active during the Eecent period, there are not now (ex- 

 cept in the neighbourhood of Ohaeawai, where yet there are 

 thermal springs) any signs of activity. From Waimate a 

 number of crater-cones encii'cle the western and southern 

 limits of the Waitangi watershed. The most beautiful and 

 perfect of these is Paeroa, situate — or rather, built up — on the 

 southern side of the Pakaraka Plain. 



Prior to the first eruptions of Paeroa, the site of the future 

 mountain was a. nearly level plain extending from Ohaeawai 

 east through Pakaraka to the north-west of Turntable Hill 

 and the range of hills of which it forms a part. The cone itself, 

 and the lesser scoria hills that lie at its base to the north-east 

 and east, are chiefly, if not wholly, scoria, which appears as 

 a coarse breccia or scoria-ash of liner grain. The solid lava- 

 streams from this crater lie on the south and south-west sides 

 of the mountain. To the east, for the distance of a mile from 

 its base, the scoria-beds form numerous small hills, and 

 together form a ridge of higher gi'ound, the eastern end of 

 which abuts against a higher ridge of Cretaceo-tertiary rocks 

 and a second volcanic cone which has arisen in that direction. 

 This barred the flow of water which originally had its course 

 to the north between the site of Paeroa and the Cretaceous 

 hills to the eastward. Barred thus, the waters from the hills 



