Overview
Sun. Nov. 2.
A fine morning with fog rolling up from north. Left at 5.12 am on bike for an excursion to the Northern end of the Oruawharo Ridge, via Rangitoto Road. Collected more fossils at the gravel pit + made additional detailed sketches of the cross-bedded sands. Reached Wall’s woolshed at 6.35 + left bike. Followed course of Maharakeke which flows in well-developed incised meanders
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and then ascended spur leading to Trig 1283'. Took a 1/4 pl. panoramic photo (2) from the limestone capped hill northeast of Trig 1283' of some of the sugarloaf peaks (A.B. + main ridge) of the Oruawharo Ridge showing "continuous scarp" in background on left + the reversed limestone outcrop (dipping east) on right. This reversed limestone bed + west-facing scarp appears to be due to the uplift of the Oruawharo Ridge. Reached Trig 1283' at 7.25 + took bearings of peaks of Oruawharo Ridge + with compass for mapping purposes. Descended west slope of Trig (slump topography) to a saddle between it + Oruawharo Peak W. Crossed spur of W. to another saddle between two tributaries of the Maharakeke + then round west of peak U. Here I found a group of boulder-like blocks of very hard blue greywacke, rusty on the surface + exhibiting exfoliation + joints. Parts of these blocks are quite smooth as a result seemingly of wind erosion + and the rubbing of stock. The weathered surfaces seem to show lamination but on freshly fractured surfaces it is quite invisible. The slopes of the high peak U show weathered outcrops of a very fissile rock apparently a fine grained indurated sandstone or a mudstone, quite unlike the hard blue greywacke. Continued round west of U and descended into the gorge of the Maharakeke tributary lying between it and the "continuous scarp". This gorge is cut in
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the mudstone strata + just above the junction of a large affluent, I found an outcrop showing distinct strata, an alternation of mudstone and slate, both much weathered and dipping west 55°. The hard blue Greywacke thus overlies the strata of the Oruawharo sugarloaf peaks, + the series is evidently an inlier of Jura-Triassic rocks identical with those which form the Tararua + Ruahine Ranges. Reached junction of streams at 8.20 + proceeded up the affluent mentioned above. The Mesozoic strata is overlain a little distance upstream by the Tertiary beds but no clear junction was visible. Continued round west side of peak B, passing first a few blocks of greywacke + then a large number of them embedded in the crest of a comparatively low ridge running along the west side of + parallel to the high Oruawharo Ridge. In close juxtaposition with the peculiar greywacke blocks, the crest of the low ridge consists of cream-coloured thin-bedded sandstone in situ – this is a very strange occurrence but the 'hard' blocks + soft sandstone beds must be the unweathered + weathered portions of the same rock. Proceeded round the west side of peak A. The low ridge with blocks of greywacke on its crest occurs here also + there are some bare surfaces of the soft cream sandstone. A few of the boulder-like blocks rest on the sandstone +
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one, the largest, is perched on a pillar which owes its existance [sic] to the protection afforded by the block, while the surrounding surfaces have been lowered presumably by wind action. Took a 1/4 pl. photo (3) of the perched block showing main Oruawharo Ridge in background. The several conical peaks of the Oruawharo Ridge are separated from each other by the gorges of tributaries of the Maharakeke rising in the "continuous scarp" The origin of this transverse drainage is a problem but it may be of the superimposed variety though it is also possible that the gaps between the Oruawharo peaks are very ancient features resurrected by comparatively recent erosion. Reached flat at top of gorge north of peak A at 9.12. At the head of the dry gap between peaks K + L, I solved the problem of the relation of the hard, blue Greywacke to the soft cream-coloured sandstone by finding an outcrop of the latter containing a lump of the former embedded, the two grading into each other. Nearby were one or two hard blocks lying on the surface of the ground. From near of gap between L and main Oruawharo Ridge, I took a 1/4 pl. photo (4) of the gap showing a young channel cut in its floor by euphemeral [sic] torrent. Proceeded through the gap + round eastern fork of peaks K, L. East of the Oruawharo Ridge the transverse tribs of the Maharakeke flow in incised meanders but
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no clear sections were seen. The characteristic topography 'of limestone outcrops' however, is here reversed, the backslopes dipping east not west + the scarps face the Oruawharo Ridge, i.e. face west, not east. Further on I found a limestone outcrop dipping east, apparently at an angle of 45°, + on reaching the prominent limestone outcrop on east side of peak A, the suspected direction of dip was confirmed, vrng [veering?] east 'or southeast' at angles of from 20° to 25°. This limestone outcrop is composed of largely of Ostrea (small) but there are also bands of compact cream-coloured granular limestone. In one place I noted a thin bed of fine large pectens with large barnacles attached. The most extensive scree or shingle slip (very finely triturated detritus) occurs on the eastern face of peak A. Took a 1/4 pl. photo (5) of scree + big limestone outcrop. On the lower course of the Maharakeke tributary which crosses the Oruawharo Ridge between the peaks U, B + A there are a number of remarkable narrowed spurs, the stream flowing in a series of intricate incised meanders. Some of the small tributary streams flow underground their courses being marked by a succession of miniature swallow-holes. Drew a rough section of the Maharakeke valley at a point just above Wall's woolshed showing it to possess a synclinal structure. The terraces are cut in a former infilling of reddish
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gravels (fossiliferous in places) + the lowest terrace is capped with about 8ft of fine alluvium. Reached woolshed at 11.20am. Home in time for dinner – Frank Goulding came to dinner but left early in pm. Maud + I went for a walk over the farm in the refreshing breeze + got as far as the manuka patch. In evening we looked at the big illustrated Bible. Gertie went to church with Mrs McSporran + A. Cattenach + brought the latter to dinner afterward.