1922 .] 
Departmental Report. 
311 
DEPARTMENTAL REPORT. . 
On the Geological Survey of the Whangarei and Bay of 
Islands Subdivision. 
By H. T. Ferrar, M.A., F.G.S., N.Z. Geological Survey. 
The systematic survey of the North Auckland Peninsula had been pending 
for a number of years, but it was not until November, 1919, that circum¬ 
stances allowed this work to be undertaken. 
Two field seasons were occupied in the examination of an area which 
has been called the Whangarei and Bay of Islands Subdivision. . The 
boundaries of the subdivision are arbitrary, and include the following 
survey districts : Whakarara, Kerikeri, Kawakawa, Bay of Islands, Russell, 
Whangaruru, Hukerenui, Opuawhanga, Purua, Whangarei, Taiharuru, 
Taranga, and a small part of Ruakaka — in all an area some 1,095 square 
miles in extent, within the Whangarei and Bay of Islands Counties. 
Mr. J. A. Bartrum, M.Sc., of Auckland University College, assisted 
with the field-work for two months during the first field season, and 
Mr. W. H. Cropp, A.O.S.M., for six months in the second season. 
The Objects of the Survey. 
The objects of the survey were primarily utilitarian. Coal has been 
exported from the district for more than fifty years, but the once well- 
known Kawakawa Mine closed down many years ago, and in later years 
other mines have shown signs of exhaustion. Hence one of the chief objects 
of the survey was to delineate the boundaries of the known coal-bearing 
areas; further, by a study of the conditions under which workable seams 
of coal occur, to determine the localities which might hold hidden coal¬ 
beds. Other objects of the survey were to study the occurrence of minerals 
of economic value, and to gather material relative to the productivity of 
the soils and thus construct a soil-map of the district. 
In order to know the conditions under which workable coals occur if 
is necessary to determine the stratigraphical succession. The sequence of 
the younger rocks in North Auckland had long been a puzzle to geologists, 
but it is thought that the jiresent survey has rightly interpreted the field 
evidence, and the following notes will deal mainly with this geological 
interpretation. 
Outline of the Geological History. 
The subdivision, with an average breadth of about sixteen miles, extends 
south-eastwards from the Cavalli Islands for a distance of seventy miles 
to Bream Head. Two types of country may be distinguished—namely, a 
continuous belt of highland country bordering the coast, and a belt of 
lower hilly country on the inner (or south-west) side of this highland belt. 
The first is a crust-block or series of crust-blocks consisting of shattered 
and crumpled Trias-Jura sediments ; the second is a downfaulted and 
down warped area covered, as in other parts of New Zealand, by Cretaceous 
and Tertiary deposits, through which rise smaller block mountains of the 
Mesozoic rocks. 
From the fact that remnants of the Notocene deposits are found scattered 
upon the surface of the higher mountainous belt we know that what is now 
North Auckland was depressed below sea-level in later Mesozoic times. 
Upon this Mesozoic sea-floor were deposited conglomerates, impure lime¬ 
stones, and claystones, conveniently referred to as the Onerahi formation, 
since the lower beds are developed in the neighbourhood of Onerahi. 
