Bartrum. — West port-Charleston High-level Terraces. 261 



worked on at least six different terraces. All of these show evidence of 

 former wave-action not only in the character of the covering alluvium, 

 but also in the characteristic planing of the hard gneiss and overlying soft 

 Miocene lignite-bearing beds into remarkably uniform terraces, with here 

 and there a residual undestroyed hummock of gneiss. In nearly all cases 

 gneissic rock forms a protective barrier on the seaward side of the terraces, 

 and where this has been absent — for example, near the mouth of the Waita- 

 kere River — the removal of the weak beds underlying the Miocene lime- 

 stone has been more complete, and beach deposits attain a thickness of at 

 least 150 ft. in the locality mentioned. 



As has already been suggested, the peneplained surface of gneiss on 

 which the Miocene beds of the Charleston were deposited did not have its 

 inequalities entirely reduced. It appears, however, from various details of 

 evidence that a great part of the present irregularity of the exposed fossil 

 peneplain, forming a large part of the surface of the coastal strip south of 

 Charleston, is due to the displacement of small earth-blocks along unim- 

 portant fractures, trending probably in a north-west and south-east direc- 

 tion. These accompanied a tectonic movement in which the beds were 

 broadly arched into a south-eastward plunging anticline. This fact is 

 demonstrated by the uprise of the base of the limestone band, in a direct 

 line between its outcrops in the Waitakere and Fox Rivers, from approxi- 

 mately sea-level at these localities to an altitude of about 500 ft. or 600 ft. 

 near the Four-mile River. Similar tectonic movements are abundantly 

 evidenced in all parts of the Buller Coalfield ; it is probable that the earth- 

 stresses giving rise to them have continued in operation to the present day, 

 and are those responsible for the severe earthquakes* experienced in the 

 district in February, 1913, which were due to the subsidence of an earth- 

 block several miles south-west of Cape Foulwind. 



Resume op Post-Miocene Geological History. 



From the fact that small quartz-pebble bands are present in the upper 

 *' Blue Bottom " near the Paparoa Range, in the valley of the Waitakere 

 River, it appears that the present western slopes of the range must have 

 been not. far from the old land of Upper Miocene times. Of the shore-line 

 of this old land nothing definite is known. Orogenic movements, which 

 had already caused warping and unconformity between the bituminous 

 coal-measures and the succeeding Miocene beds over a considerable portion 

 at least of the West Coast area, became again active at a period post-dating 

 the close of Miocene sedimentation, and the uplift of the Paparoa block 

 relatively to the coastal earth-block resulted. The question whether the 

 whole area of Miocene deposition was uplifted in loto before faulting 

 occurred, or whether uplift was relative in the various earth-blocks, need 

 not be discussed here. 



In post-Miocene times the upper strata of the weak " Blue Bottom " 

 sandstones north of the Little Totara River were planed off by wave- 

 encroachment back to the barrier afforded by the resistant granitoid rocks 

 of the Paparoa Mountains, whilst south of the Little Totara the limestone 

 proved an effective barrier to the advance of the sea. Upon this wave-cut 

 platform the gravels of the " 500-foot " terraces were deposited. Prior to 

 the formation of this plain of marine erosion, now buried below the gravels, 

 uplift varied by standstill, and perhaps by slight depression, had been in 



* Hogben, G. : Paper read before the Wellington Philosophical Society, 24th Sep- 

 tember, 1913 (see p. 301 of this volume). 



