274 Transactions. 



chemical composition would probably be much the same as that of the 

 Oamaru brown coals of to-day. During the period that has elapsed since 

 the Miocene, further chemical change has doubtless taken place both in the 

 Eocene coal-seams and in the pebbles derived therefrom. 



The extracts from McKay's reports of 1877 and 1901, as well as the 

 writer's own observations, completely dispose of the suggestion that " the 

 coal fragments were wood when entombed in the mud and . . . have 

 been changed into coal in situ."* It is true, as already mentioned, that 

 fragments of carbonized wood are associated with coal pebbles in the Buller 

 Gorge conglomerates, but these may nearly always be distinguished from 

 the true coal by their shape, by their more rotten character, and in most 

 cases by distinct traces of woody structure. 



Marshall has also suggested contemporaneous erosion of neighbouring 

 coal-seams as a possible cause for the presence of water-worn coal in the 

 Lower Oamaru beds. It has, however, already been stated that the coal- 

 pebble conglomerates of the Buller Gorge are older than the chief Miocene 

 coal-seams, and that the water-worn coal does not agree in composition 

 with them. There is, moreover, no independent evidence of contemporaneous 

 erosion of Oamaru coal-seams, and in any case, at the time when the Omotu- 

 motu beds were formed, it is not likely that any Miocene accumulations 

 of vegetable matter were consolidated to a coal sufficiently firm and free 

 from moisture to withstand ordinary erosion and transportation by water 

 without complete disintegration. 



Before Eocene coal-seams could be eroded, faulting or folding move- 

 ments must have elevated portions of the bituminous-coal measures near 

 Greymouth at least 2,000 ft., and more probably 3,000 ft. At Seddonville 

 an elevation of 1,500 ft. might have sufficed. Of an inter-Eocene move- 

 ment on this scale there is no trace. Certainly there was no defined fold- 

 ing ; and though it is just possible that elevation of part of the bituminous- 

 coal measures may have taken place whilst the remainder continued to 

 subside, and was conformably covered by Miocene strata, it is much more 

 likely that the whole area on the west coast of the South Island containing 

 Eocene strata was more or less affected. In any case, it must be admitted 

 that elevation extended from Greymouth to Seddonville, and for some 

 distance north and south of those points. It would then follow that the 

 Miocene rocks in that area rest unconformably upon the Eocene. 



B. Discordance in Dip between Eocene and Miocene Rocks. 



Ordinarily, discordance of dip between the Eocene and the Miocene 

 rocks cannot be proved, and it is evident that no marked folding of the 

 bituminous-coal measures took place prior to the Miocene in areas where 

 beds of the latter age are now present. In all probability, however, there 

 was block-faulting similar to the faulting that has taken place since the 

 Miocene } and this may have been accompanied by tilting, with the pro- 

 duction of relatively steep dips near the fault-planes. Such tilting may 

 be responsible for a discordance in dip observed at Brighton, thirty miles 

 by road south of Westport, where Miocene strata, containing a seam of 

 lignite or brown coal near their base, rest on a breccia or breccia-conglome- 

 rate similar to the Hawk's Crag breccia in the Buller Gorge. McKay states 

 that the relations of the lignite beds and the breccia are decidedly uncon- 



* Marshall, op. fit., p. 68. 



