MOROAN. — Thf- Iff neons. Itarl-x of the W ailii Gohlfehl. 259 



The term " auriferous series " may be applied to the rocks in question as a 

 non-committal name with respect to their petrographical character. There 

 is as yet no very positive evidence available concerning the age of the auri- 

 ferous series, but it may be assumed as Eocene, or possibly early Miocene. 



After the rocks of the auriferous series had been subjected to more or 

 less denudation, and very probably to the internal change known as propy- 

 lization, a limited amount of material accumulated in valleys or other 

 hollows that were doubtless occupied by lakes. Such material, in the form 

 of well-stratified tuff, is exposed in the Grand Junction A or No. ] shaft 

 at a depth of 620-640 ft. below the surface, and about 240 ft. below present 

 sea-level. 



Soon volcanic activity on a large scale was resumed, and a second great 

 outpouring of andesitic lavas took place. These rocks form high hills to 

 the north of Waihi, and appear oji the surface in the open valley west of 

 Martha Hill. They also occur to an unknown extent under the younger 

 rhyolitic rocks at and near Waihi. In point of age these younger andesites 

 and their accompanying tuft's (developed only very slightly near Waihi) 

 may be referred to the Beeson's Island group of McKay, or to Eraser's 

 " Tertiary Volcanic Rocks of the Second Period." To the Beeson's Island 

 group may also be assigned the great development of tufts, in places much 

 intersected by dykes, seen along the coast east and north-east of Waihi. 



After the eruption of the " Second Period " volcanics a comparatively 

 brief period of rest from igneous activities was followed by the outpouring 

 of acid lavas. Some of these were rhyolites of the peculiar brecciated- 

 looking ty]De known as " wilsonite " (11,* vol. 1, pp. 123, 124 ; vol. 2, pp. 46, 

 138). This rock forms the greater part of the so-called " Waihi Plains," 

 and wraps partly round the outcrops of the auriferous series. With it 

 are associated small amounts of tuft. 



Between Waihi and the coast there appear spherulitic rhyolites, pro- 

 bably of approximately the same age as the wilsonite, but possibly older. 

 These are well developed east and north-east of Waihi. They are seen on 

 the coast north of Houmunga Bay, at Waihi Beach (where they contain 

 auriferous veins), and at Mount Hikurangi, a conspicuous elevation a few 

 miles south of Waihi. 



Breaking through the wilsonite in various places, and therefore of younger 

 age, are light-coloured rhyolites of harsh texture. These are observable 

 mainly in and near the Town of Waihi, and are also well seen near Wai- 

 kino, four miles to the west. 



The various rhyolites may be provisionally regarded as of Pliocene age, 

 and as contemporaneous with the great rhyolitic flows of the central part 

 of the North Island. 



Some hornblende-andesites that occur near Waihi are younger than 

 any of the other andesites, but their age with reference to the rhyolites 

 is uncertain. 



The recent surface accumulations of the Waihi district, consisting of a 

 little conglomerate, talus, clay, &c., are of little moment from a purely 

 geologic point of view. The loamy clay on the slopes of the Martha Hill 

 is apparently largely of aerial origin, and might therefore be called loess. 

 Since this material furnishes a cheap and efficient " filling " for the Waihi 

 Mine workings it has considerable economic value. 



* This and other numbers similarly inserted in brackets refer to list of literature 

 at end. 



9* 



