48 Transactions. 



Art. V. — The FUnt-heds associated ivith the Amnri Limestone of Maii- 



horoiigh. 



By J. Allan Thomson, M.A., D.Sc, F.G.S., Director of tlie Dominion 



Museum, Wellington. 



[Read before the Wellington Philosophical Society, 27th October, 1915.] 



Plates II, III. 



Contents. Page 



I. The Amuri limestone 

 II. Distribution of the flint-beds 



III. Character of the flints 



IV. Origin of the flint-beds 

 List of papers referred to 



48 

 52 

 53 

 55 



58 



I. The Amuri Limestone. 



The Amuri limestone, which takes its name from Amuri Bluff, seventeen 

 miles south of Kaikoura, is a great limestone formation composed of a 

 variety of rocks, of which the most characteristic and the mo.st abundant 

 is a much-jointed, thin-hedded limestone of chalky appearance, but con- 

 siderably indurated and much harder than chalk. Typical soft chalk is 

 known from the formation only at Oxford, in Canterbury, near the southern- 

 most part of its range.- In North Canterbury the lower beds of the lime- 

 stone are generally softer and more argillaceous, with a coarser and more 

 conchoidal fracture, and pass down gradually in the Waipara district into 

 a dark-coloured niudstone. In East Marlborough, where the formation is 

 very much thicker, there are several coarse alternations of hard chalky lime- 

 stone with more argillaceous bands, and in places there are fine alternations 

 of hard white limestone with greenish argillaceous limestone, in all cases 

 fine-grained. The base of the formation in this district is formed by the 

 beds of flint which form the subject of this paper. By its fine grain and 

 chalky appearance, together with the manner in which it breaks into small 

 cuboidal blocks, the Amuri limestone is easily distinguished from all other 

 limestones in New Zealand,* and it has evidently had a different mode of 

 origin from the Oamaruian (Ototaran) limestones of Otago and South 

 Canterbury, which are largely composed of fragments of Bryozoa. It con- 

 tains a fair proportion of unbroken tests of Foraininifera, especially 

 Glohigerina, but the greater part of its mass is made up of an exceedingly 

 fine-grained calcareous mud, with little terrigenous matter. Analyses, 

 however, reveal a considerable amount of silica, which must also be present 

 in a state of minute subdivision, while there are occasionally grains of 

 glauconite. 



Although the Amuri limestone is now distributed in an irregular and 

 discontinuous manner throughout the east part of North Canterbury and 

 Marlborough, there can be little doubt from its lithological characters that 

 it once spread over the greater part of these districts, a conclusion previously 



* Cf. Hutton, 1877, pp. 27-58. 



