MansnHALL.— The ** Hydraulic Limestones " of North Auckland. 617 
The “Hydraulic, Limestones " of North Auckland.* 
By P. Мавѕнли, M.A., D.Sc., F.G.S., F.N.Z.Inst., Hutton and Hector 
Medallist. 
[Read nd ан piece or Institute of Canterbury, 5th December, 1923 ; "E received by 
1923 ; issued separately, 28th August, 1924.] 
A CONSIDERABLE amount of discussion has taken place in regard to the 
age of this formation. It is not intended in this paper to review the 
opinions that have been expressed in regard to this өн, and it will 
to it a Lower yes age. At the present time it is merely intended em 
mention oi facts not previously adduced which favour the author's 
contentio 
The “ занак limestone " is, generally speaking, а foraminiferal lime- 
stone which covers large areas of the North Auckland Peninsula between 
it frequently contains also a great many remains of organisms that had 
. siliceous skeletons—sponges, diatoms, and Radiolaria are included amongst 
these. The iari often contains a good deal | of wea and some- 
by a great und er of crevices and joints, and slide ily, even on country 
with gently чар. relief. It has been su on to considerable earth- 
were shown in a case by the Wilson’s Cement Company. These specimens, 
however, have never been described, and appear now to be lost. Some 
stratigraphical rem have lately been noted and require a definite 
statemen 
(1.) At Pahi the hydraulic limestone is clearly seen to overlie a green- 
sand. This is very clear on the shore-line of the eastern side of the Pahi 
arm of the Kaipara Harbour, between Whakapirau and Jackman's, where 
the rocks dip about 30? to the south-west and strike to the north-west. 
(2. On the hill between Pahi Township and the Arapaoa arm of the 
Kaipara Harbour it is found that all the eastern and = parts of the 
hill are formed of limestone, while greensands crop out at the bottom of 
the western and southern sides. On the west side and on the south the 
сарана have а generally easterly dip. The obvious conclusion is that 
e greensands dip under the hydraulic limestone. Although the slope of 
the hill near the base is covered with detritus, the dip of the rocks shows 
that their relation is properly represented by the diagram fig. 1—the same 
t Jackman's, mentioned previously, which is about one mile 
distant. 
If the shore-line of the Arapaoa arm is followed to the north-west for 
about one mile, a syncline is found exposed on the foreshore of the harbour 
* For a map of the locality see MARSHALL, Trans. N.Z. Inst., vol. 49, p. 435, 1916. 
