150 Transactions. 
in some instances, though not in others, as a deposit in former swamps. 
It was noted that the nodular masses often lie upon the exposed surface 
overlying material and it is probable that seepage of water rich in iron 
salts along such junctions has given rise to their formation. 
IcNEOovs Rocks. 
It is unnecessary to add further description to such mention as already 
has been made of the igneous rocks represented in the Waitemata con- 
glomerates, and this section will therefore be reserved for a brief statement 
of such other igneous rocks as have been found. The majority occur 
as intrusions of ultrabasic character penetrating Onerahi rocks, and are 
described in the next paragraph. In addition there are several other less 
important occurrences which will be described. 
Ultrabasic Intrusives. 
This series of rocks, which can broadly be ena ——— abund- 
antly intrude Onerahi limestones and clayston The m themselves 
are not sufficiently resistant to form (UMEN 1 pe any dogs nspicuous in 
their erin to topography, and they are therefore оет ошу Бу 
patient search. 
The ооа ате the main occurrences 
a.) On the east and north-east slopes of F Flat-top Hill. 
(b. ) Alorigside the Parakakau-Silverdale Road, a short distance from its 
junetion with the Parakakan. Kaukapakapa Road, there is a large 
interesting mass which een extensively quarried. A small 
intrusion of serpentine can dices be seen on the same road, near 
where it gains the summit of the divide between the Orewa and 
Kaukapakapa drainage basins. 
(с.) Farther along the Parakakau-Silverdale Road serpentine outcrops 
near the cemetery shown on the map. The main body has been 
сабой west of the short branch road giving access to the 
осебе, but it can be traced in much-weathered state farther 
(d.) East p White Hills School there is an outcrop adjacent to the Silver- 
kw le Ro = on Mr. Davidson’s farm, but it was not examined by 
e wri 
(e.) hon White ‘Hills School there are several exposures representing 
apparently the one intrusion. The rock is exposed in the road- 
cutting near the school, and in several places north-westwards. 
At one of these latter outcrops a quarry has been opened up. 
(f.) About a mile west of White Hills School. 
(g.) On the valley-slopes of a small stream separating Wray's house 
from the school at Horseshoe B 
Most of the intrusions recorded are represented on the фебошредушЕ 
map in their approximate positions. 
this was written a short report by Mr. H. T. Ferrar upon the Silverdale 
PD. TP" Ann. Rep. N.Z. Geol. Surv. (n.s. е 1923, р. ^ has a grew red, in which it is 
stated that the serpentines underlie the Onerahi beds, The evidence submitted i 
unconvincing, and the supposition raises many more difficulties. than it attempts to 
remove. 
