Bartrum.—Geology of Riverhead-Kaukapakapa District. 141 
in Progress Reports are practically the only other joda to the geology of 
the district that the writer has come across in the i tae of the Geological 
urvey. He himself has recently described a varie of rocks from con- 
glomerates outcropping near Albany and Riverhead facet 1920). 
SYNOPSIS OF STRATIGRAPHY. 
The denos ДЕЧ units are recognized : (1) Onerahi series ; 
(2) Waitemata series; (3) Andesitic ойне formation; (4) Plei sto- 
cene and Recent "epos ts. 
e oldest rocks, which constitute the Onerahi series, include a pro- 
m bed, generally spoken of as the “ hydraulic limestone," which is 
a mpi Pon argillaceous, fine-grained, non-crystalline limestone. ‘It most 
Ar represents an oceanic ooze rich in Globigerina, but is associated 
es shaly claystones and indurated siliceous "inudslonee, which seem 
n part wd represent a local variation of the limestone and in part 
interbedded wit The series-name selected is that introduced by Ferrar 
Whangarei district. ere is no intrinsic evidence of age in the beds 
themselves, but their provisional Cou doge assignment to the Cretaceous 
period may be taken as approxim dips rect in the light of evidence 
obtainable in the Kaipara area farther n 
Above the Onerahi rocks—the facts ей аса ан is an 
extensive series of argillaceous sandstones with minor interlaminated mu 
stone, which outcrop continuously southwards on "the shores of Waite- 
mata Harbour, but much less prominently in the northern part of the 
rep oreet -Riverhead district. These beds belong to the Waitemata 
series, which appears from its fossil content near Auckland to be a 
mately Upper Miocene in age. In the area now mapped there are locally 
nature forming part of the series. Northwards beyond the present area 
the massive sandstones are especially well developed. 
The next formation in upward sequence consists of andesitic conglome- 
rates and breccias, limited in extent to the north-west corner of the district 
now described, but traceable northwards, and also southwards where they 
build the Waitakere Hills, which border the west coast for many miles near 
Auckland. They appear to lie conformably upon sandstones of the Waite- 
mata series in the few places ud fairly clear sections are obtainable, and 
thus are regarded as approximately Upper Miocene in age. Pleistocene 
панов do not show an ierit phase in their history. 
Recent deposits are limited to linear swamps along the courses of slow- 
flowing streams. aen are a constant feature of most of the valleys, but 
are by no means extensive. Occasional bog iron-ore deposits of small size, 
more extensive than die here in small north-east-flowing tributaries of 
Gibbs Creek, a middle right branch of Rangitopuni Stream, are probably 
Recent in age. 
he synopsis is completed by mention of intrusive igneous rocks. Of 
these there are two series: one comprises ultrabasic intrusions which now 
are represented by serpentinous rocks, and the other rocks of semibasic 
character. The first invade Onerahi beds, and have not yet been observed 
above that horizon; the others do not constitute a composite series, and 
differ in age. 
