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Art. XXXV. — The ( 'oalfields of West Nelson ; ivith Notes on the Formation 



of the Coal 



By J. Henderson-, D.Sc, A.O.8.M. 



Communicated by Professor James Park. 



[Bcod before the O/w/o Institute, 4th October, 1910.] 



At the begiiiniiig of the coal period what is now west Nelson consisted of 

 the same series of earth-blocks as now. These blocks had been subjected 

 to denudation, and parts of the elevated blocks had been reduced to the 

 same level as the depressed blocks ; consequently, when depression of the 

 whole took place, conglomerates and sandstones Avere deposited not only 

 on those blocks with a tendency to sink, but also on the lower portions of 

 those blocks with a tendency to rise. 



A pause in depression permitted vast swamps and forests to envelop 

 the coasts ; it is possible that the centres of the valleys were still under 

 jvater. Further sinking caused the vegetation to be smothered by deposits, 

 and repetitions of the processes have produced other seams. The gradual 

 filling-in of the central deeper portions of the graben valleys would permit 

 of the higher seams overlapping the lower in that direction, while the 

 sinking of the land would produce overlap in the other. It is thus possible 

 that the higher seams may extend right across a valley, while the lower 

 thin out toward the centre ; perhaps all the seams so thin out. Where the 

 main drainage-channels crossed the vegetation-fringe the coal-seams are 

 likely to thin out and become impure. Again, it is conceivable that dif- 

 ferent portions of the coastal fringe, by reason of differential sinking and 

 differential filling, would become fit for vegetable growth at different times. 

 When all is considered, it seems probable that the coal should occur as 

 seams thinning out in all directions, and that the beds should overlap each 

 other in a great variety of ways. The coal has not yet been sufficiently 

 worked to prove these contentions, but the seams of Denniston, Reefton, 

 and Greymouth appear to conform entirely with them. 



The hypothesis which considers coal-seams as altered accumulation of 

 drift vegetable matter finds support in west Nelson, in that the coal 

 frequently rests on hard rock without the interposition of fireclay ; fm'ther, 

 the fireclay bands occur indifferently at the bottom or the top of the coal- 

 seams. Again, water-worn pebbles occur in the coal at Point Elizabeth. 

 The distribution of the seams is perhaps more readily explained by this 

 than by the groAvth-in-place hypothesis. On the other hand, if the seams 

 have been formed from drift some at least should occur intercalated with 

 marine beds. This does not seem to be the case, and the beds immediately 

 associated with the coal appear to be either estuarine or lacustrine. 



Coalfields. 



The thrusting-up of what are now the peneplains, but what in Miocene 

 tnnes were base-levelled islands, through the surrounding coal-measures 

 permits of a somewhat arbitrary division of the coal-areas into coalfields. 



The Whakamarama* Coalfield comprises the coal lying to the west and 

 north of the Whakamarama peneplain. It may be conveniently subdivided 



* Hochstetter : " New Zealand," pp. 58, 84, 85. Hector : Geol. Surv., No. 4, p. 18 

 ct ieq. ; No. 19, pp. ix-xiii. Cox: Geol. Surv., No. 15, pp. 71-73. Park: Creol. Surv., 

 No. 20, pp. 52-57, 200-5, 237-41. Mackay : Paper.s and Reports relating to Minerals, 

 1900, C.-6, pp. 1-5. 



