Morgan. — Unconformities in Stratified Rocks of West Coast. 271 



I. The Post-Miocene Unconformity. 



The first unconformity shown in the table of formations is typically a 

 comparatively short break between Pliocene and Pleistocene, and represents 

 a time during which the whole westerly part of the South Island was being 

 rapidly uplifted. Elevation, however, had begun at an earlier epoch — 

 probably before the close of the Miocene — and with the exception of several 

 periods of rest and one well-marked period of depression (near the end of 

 the Pleistocene) has continued till Recent times. Moreover, besides being 

 spasmodic, elevation has been differential in the extreme, block-tilting and 

 faulting being prevalent, so that whilst some areas — for example, the Paparoa 

 and Brunner Ranges — were probably uplifted 5,000 ft. or even more,* others 

 remained almost stationary. These differential movements are roughly 

 reflected by the varying extent of unconformity. Thus in many places 

 Recent gravels rest on Upper Miocene claystones (Blue Bottom), or on 

 still older rocks. At Cape Foulwind horizontal Pleistocene sandstone of 

 marine origin overlies an eroded surface of gently dipping Miocene rocks. 

 In various parts of the Greymouth district unconformity between Moutere 

 or Old Man gravels of Pliocene age and Pleistocene gravels is generally 

 indicated merely by the latter resting on an eroded surface of the former 

 without any noticeable discordance of dip. The plane of contact is usually 

 marked by a layer of large stones, evidently residual from the denuded 

 portion of the Moutere gravels. On the other hand, in a few places a decided 

 discordance of dip may be seen, the most notable instance being at Healy's 

 Gully, north of Blackball, where nearly horizontal Pleistocene gravels rest 

 on steeply dipping Pliocene beds, which are involved in a great fault.f 



II. The Post-Eocene Unconformity.] 



The unconformity between the bituminous - coal measures of Eocene 

 age and the Miocene or Oamaru rocks presents peculiar features, and will 

 therefore be fully discussed. It was announced by the writer in 1909, J 

 but since then its existence has been questioned by Marshall, § partly on 

 the ground that no direct stratigraphical evidence of unconformity has been 

 discovered, and partly for other reasons. The problem is one of great 

 importance, particularly from an economic point of view, for its solution 

 bears directly upon the question of boring for bituminous coal beneath 

 Oamaru rocks near Westport and elsewhere. 



The evidence for the existence of a post-Eocene unconformity, including 

 data recently obtained, may be classified as follows : — 



A. The Miocene rocks contain water-worn pieces of coal and carbon- 

 aceous shale almost certainly derived from the bituminous-coal measures. 



* The total uplift since the Eocene is known to have reached 6,500 ft. in places, 

 but some of this may be ascribed to pre-Miocene elevation : tee a later page. If there 

 is no unconformity between Eocene and Miocene, the maximum uplift approaches 

 10,000 ft. 



f P. G. Morgan : " Geology of the Greymouth Subdivision, North Westland," 

 Bull. No. 13 (n.s.), N.Z. Geol. Surv., 1911, p. 74. 



| Third Annual Report of N.Z. Geol. Surv., Parliamentary paper C.-9, 1909, p. 13. 

 (See also Bull. No. 13 (n.s.), 1911, pp. 65-66. and earlier reports by McKay cited on 

 later pages.) 



§ " New Zealand and Adjacent Islands " (reprinted from " Handbuch der region- 

 alen Geologie "), Heidelberg, 1912, p. 68. (See also " The Younger Rock-series of New 

 Zealand," by Marshall, Speight, and Cotton, Trans. N.Z. Inst., vol. 43, 1911, pp. 392-93.) 



