Hbndersom. — Surface Forms and DraitKKjr-si/stenis of \\'t.<f ydson. 807 



forming a group of block mountains analogous to those in Otago,* except 

 that, having been subjected to the more active denudation-conditions ob- 

 taining in this portion of New Zealand, they have been more thoroughly 

 dissected. At present only the comparative equality in height of the higher 

 peaks indicates the ancient peneplanation. 



Faults. 



There are, then, two elements in the geography of west Nelson — the 

 peneplains and the rift-valleys — and the limits of both of these are generally 

 determined by poAverful faults. There are two groups of normal down- 

 throw faults, separated by the great alpine overthrust, those lying to the 

 west of this overthrust belonging to west Nelson, and those to the east to 

 the alpine range. 



The main structural fault of west Nelson, and, indeed, of the South 

 Island, is the great alpine overthrustf which runs from Foveaux Strait to 

 D'Urville Island. This overthrust follows the Gregory Valley of Morgan, t 

 which may be traced from Lake Kanieri to Lake Rotoiti.§ Its course has 

 been indicated by Hectorj] and Mackay.*| On the western side of this 

 great fault have been intruded igneous magmas, which abut at intervals 

 against the overthrust from South Otago to Lake Rotoiti, in Nelson. On 

 both sides of the fault occur basic and ultrabasic intrusions of later age 

 than the granitic intrusions already mentioned. On the east side they 

 occur from D'Urville Island to Otago, forming in part the Pounamu forma- 

 tion of the Geological Survey. On the west side these rocks are represented 

 by lavas at Koiterangi and Paringa, and by dykes at many points. 



The faults of the alpine range are exceedingly numerous, and tend to 

 run either north and south or east and west.** They are often indicated by 

 hot hepatic springs, as in valleys of the Maruia, Upper Grey, Hurunui, 

 Trent, and Taipo Rivers. North-and-south faults occur in the Upper 

 Taipo, Otira, Waikite, and Trent. East-and-west lines of faulting — perhaps 

 hlatten — are followed by the Upper Taramakau and Hurunui, the Waiheke, 

 and Doubtful, the Marchant, Upper Grey, Maruia, and Henry Rivers. 

 The Wairautt fault is different from the faults of the alpine peneplain, 

 hitherto considered : it has a more easterly trend than either the main 

 alpine overthrust or the great faults of the Kaikouras and North Island 

 ranges — it is, in fact, a connecting-link between these two great parallel 

 systems of breaks. 



The faults to the west of the alpine overthrust tend to run in two 

 directions — north and south, and north-east and south-west.J| The first to 

 be considered, the Motueka fault, probably skirts the coast of Tasman 

 Bay, running south from Separation Point to the mouth of the Motueka, 



*Park: N.Z. Geol. Surv. Bull. No. 2 (n.s.), p. 6 et seq. ; No. 5 (n.s.), p. 6 ei seq. ; 

 "Geology of New Zealand," 1910, p. II. 



t Mackay : Geol. Surv., No. 21, p. 20. Morgan : N.Z. Geol. Siuv. Bull. No. 6 (n.s.), 

 p. 1\ et seq. 



t Morgan : N.Z. Geol. Surv. Bull. No. 6 (n.s.), p. 38. 

 § Haast : Geol. Explor. of West Nelson, p. 94. 

 II Hector : Geol. Surv., No. 4, p. 29. 



'i\ Mackay : Mines Statement and Goldfields Reports, 1893, pp. 136, 174. 

 ** Cf. Morgan : N.Z. Geol. Surv. Bull. No. 6 (n.s.), p. 70. 

 tt Mackay : Geol. Surv., No. 21, p. 19. 



JtPark: Geol. Surv., No. 19, p. 83. Mackay: Geol. Surv., No. 21, pp. 20, 21. 

 Mackay : Geol. Surv., No. 12, pp. 124, 125, 127 (in this and in many following references 

 faulting is not definitely stated, but may be inferred). 



