Marshall. — The Tounger Limestone)^ of New Zealand. 87 



Art. VIII. — The Younger Limestones oj Netv Zealand. 



By Professor P. Marshall, M.A., D.Sc, F.G.S., Otago University. 



[Read before the Otago Institute, 7th December, 1915.] 



Plates VIII-X. 



In previous papers attention has been drawn to the great difEerence.s of 

 opinion which have been expressed and published in regard to the age of 

 the younger rocks of New Zealand. It has also been stated that it is very 

 generally the fact that in all those districts where the younger rock-series 

 is well developed there is a conspicuous bed of limestone forming one of 

 its members. In various parts of the country this limestone has been 

 placed in difierent chronological divisions by geologists. In some locali- 

 ties it has been classed as Cretaceous, in others as Oligocene or Miocene. 

 Identical beds of limestone which have by some authors been classed as 

 Cretaceous have been placed in the Oligocene or Miocene by others. The 

 statements about the age of the limestones have frequently not been based 

 upon the internal evidence found in the limestones themselves, but upon 

 external evidence found in their stratigraphical relations, or in the palaeon- 

 tological remains found in the beds above or below the limestones in 

 various localities. In some instances both of these methods have failed, 

 and reliance has then been placed upon the lithological resemblancv' of 

 some outcrop of limestone to another, often situated in some distant part 

 of the country. Up to the present time no attempt has been made to 

 describe with any degree of accuracy the minute structure of these rocks, 

 or to state even generally the nature of the organisms of which they are 

 composed. 



It is intended in this paper to make a general statement of this nature, 

 though it is recognized that a full description of the recks, with a specific 

 identification of the organic remains which occur in them, would require 

 the work of a specialist in each particular group of organisms. In the 

 case of the Echinoderms, which are very abundantly represented, the 

 remains are merely spines or isolated plates, which even in the hands of 

 an expert would not admit of accurate identification. The Polyzoa also 

 require very expert knowledge in order that they should be identified in 

 chance sections. In the case of the Foram.inifera generic classification 

 alone is attempted. The Sponges and Radiolaria, which occur more rarely, 

 are referred to in a general way only. Notes are also given on the classifi- 

 cation of these limestones by various geologists who have examined them 

 in the laboratory or in the field. 



1. Whangarei - Kaipara - Bay of Islands Eegion of North Auckland. 



Within this district limestones cover a large area of country, and two 

 distinct types have been generally recognized — the so-called hydraulic 

 limestone and a semi-crystalline type generally called the Whangarei lime- 

 stone. Near Whangarei the latter occurs at Horahora, Kamo, and Waro. 

 Near the Bay of Islands the same type is found at Waiomio, and in the 

 Kaipara area at the so-called Gibraltar Rocks at the end of the Pahi Arm. 

 The hydraulic limestone has a much wider occurrence. Typical localities 

 from which specimens have been obtained and are here described are 

 Mahurangi, Port Albert, Wellsford, Kaiwaka, and Limestone Island, in the 

 Whangarei Harbour. 



