76 Transactions. 



Art. VII. — The " Red Rocks " and Associated Beds of Wellington Peninsula. 



By F. K. Broadgate, M.Sc. 

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



Plates VI, VII. 



Introduction. 



The area examined in connection with this paper is the south-west corner 

 of the Wellington Land District, and more particularly is defined by Port 

 Nicholson on the east, and a line drawn west from the head of that inlet 

 to the coast ; Cook Strait forms the remaining boundary. The area is 

 conveniently termed the Wellington Peninsula (fig. 1). 



Red and green argillites, often with associated tuff-beds, have been 

 noted in various parts of New Zealand. The present paper gives the results 

 of an examination of these rocks as they are represented in the Wellington 

 Peninsula. Such examination must take account of the series of grey- 

 wackes and dark-coloured argillites, as interbedded members of which the 

 red and green argillites occur ; some general notes on this series precede 

 the main problem. 



The conclusion reached is that the red and green argillites were origin- 

 ally green argillites not differing, save in colour, from the ordinary dark- 

 coloured argillites. An attempt is made to explain the changes undergone 

 by the green argillites subsequently to their deposition, and a hypothesis 

 to account for the formation of such argillites is put forward. 



For convenience, the well-known name " Maitai " is here adopted for 

 the whole of the rock-series under review. No age significance is to be 

 attached to its use in this connection ; the only fresh evidence bearing on 

 this question, as related in the text., is of a destructive rather than con- 

 structive kind. 



Topography. 



The mountainous area of the Wellington Peninsula, together with the 

 Rimutaka Mountains to the east, form the southern extremity of the main 

 structural axis of the North Island. This axial line is continued in the 

 South Island by the Kaikoura Mountains, of Marlborough. 



The existing topography is that of a recently uplifted block which had 

 already sufi'ered close folding and distortion, and, according to J. M. Bell 

 (1, p. 535), had been reduced to a state of peneplanation before uplift. In 

 a report on the Maharahara district, Woodville, J. A. Thomson states that 

 the second period of general "uplift began in late Pliocene times (2, p. 165) ; 

 while A. McKay believes that " the Kaikoura Mountains . . . have 

 been elevated to their present height from a moderately elevated plateau 

 solely by earthquake action, and this since the conmiencement of Pliocene 

 times" (3, p. 11). Elevation commencing in the Pliocene, and, with in- 

 . tervals of standstill, continuing to the present day (4, p. 246), may be 

 fairly assumed to be the case in the Wellington Peninsula, lying midway 

 between the districts mentioned. 



Compressional forces acting on an area already much disturbed have 

 resulted in tilting and differential movements, with the institution of faults 

 along planes of weakness, and probably a renewal of faulting along old 

 lines. 



