POVERTY BAY 01L-BEARSHG AREA.

Gisborne Times, Volume V, Issue 104, 11 May 1901, Page 3

POVERTY BAY 01L-BEARSHG AREA.

EXTRACTS FROM THE PROGRESS REPORT OF THE GOVERNMENT GEOLOGIST.

Immediately west of Karaka (on the Gis-borne-Opotiki Road) the hills on the south side of the Waikohu Valley show sections of strata consisting of sandy argillaceous’ beds, more or less calcareous, which dip to the south, and form rounded hills that rise to a height of 400 to 500 ft above the river valley. These rocks have veins of finegrained calcareous rock that traverse the Sedimentary rocks at an angle and dip to the south-east. The dip indicates the southern wing of an anticline, running a little to the north of west, but the anticline itself could not be observed, though the crest of the same must underlie the alluvial deposits jointly brought down by the Waipaoa and Waikohu Rivers. Between five and six miles to the west of Karaka the Waikohu Valley is less in width, and at the willow crossing the beds described are to be seen on both banks of the river, and the anticline indicated maybe traced on the northern side of the valley. At the willow crossing, on the south side of the valley—the hills receding —there is between these and the riverbank a breadth of high terrace land, on the northern edge of which, near the river-

crossing, there is a heavy deposit of travertine (calcareous sinter), the supplysource of which is obscured, the waters having ceased to flow. This travertine forms massive rocks on the brow of the terrace, and sufficiently indicates the calcareous nature of the rocks drained by the spring when active. More to the west the numerous crossings of the river are all on the southern wing of the anticline, and near Mr Hutchinson’s property the hills rise to a more considerable height

lan further east, and assume the outlines

of a regular range parallel to the valleyon its southern side. The slopes of this range are abrupt, and there is a tendency to the formation of high cliffs on this side of the river, which exposes the strata still dipping south-east. On the northern side of tho valley the hill slopes are at lower angles—or with one or two exceptions are so —and the surface of the solid rock at many places is covered by slips back to

and beyond where the anticline can be determined. Though this be so, there can be no doubt that the concurrence of the southern slope and dip, back to the crest of the anticline,’ lias afforded unusual facilities towards the formation of slips. Nevertheless, the northern dipping strata bevond and above the anticline is also

ich subject to slips, and on the northern

side of the valley this condition of things con tinues to Poututu accommodation house Here the river; as followed west, trends more to the north-west a distance of übout half a mile ; but suddenly returning to tho south side of the valley, its bod crosses the strata at right-angles, and at tho last crossing, near the accommodation-houso, shows strata dipping to the north, and on tho east bank of this traverse of tho stream, just above the crossing, the anticline is clearly exposed. The beds on the north side of the anticline strike W. 10 degrees N., and dip nearly north at angles of 25 degrees to 30 degrees. From the crest of the anticline for a short distance on each side tho beds are nearly flat; but in the

high cliffs further up stream, the base of which is washed by the river, they have acquired a dip of 20 degrees to the south. Above this point the river trends to the south, and follows a tortuous course

through a deep gorge, which, after about a mile in a south-west direction, resumes a north-west course, and thus again ap-

proaches tho anticline still on the northern side of the valley. The road going west to the Motu River cuts across the bend thus formed, and follows nearly the course of the anticline, and crosses a saddle between an isolated conical hill, overlooking

the deep bend and gorge of the river, and hills of nearly equal height on the northern side. Beyond the saddle and above tho deeper part of tho gorge the river resumes its north-west course, and the road on the northern side at a high level runs parallel to the river to a point threo miles and a half beyond Poututu. During the last two miles of the distance mentioned tho road and the anticline are nearly coincident in place and direction, and for the last mile it is seen that while on the south side of

the anticline the dip is moderate, on the northern side it is at a high angle, and the beds somewhat disturbed. From Karaka to the last crossing of the river, at Poututu Accommodation-house tho higher beds of the series arc scon, but half a mile west of the last crossing of tho river dark greensands begin to appear, and these are associated with a grey calcareous rock abounding in grains of glauconite (greensand), and further west with hands of brown sandstone. On the south side of

the upper valley of the river the evenly stratified beds of the south sido of the anticline form a mountain-range rising to a height of some 1,800 feet above the valley, and from the river to the top of the range a continuous succession of tho rocks present can be traced, but the greensands on the north side of the anticline do not appear to be present. I have been at some pains to describe the mode of occurrence and position of this anticline, as from conversation with Mr It. Brett, who is interested in the discovery of petroleum in this colony, it appears that in.other countries the crest and immediate slopes of anticlinal arrangements of strata are considered eminently favorable for the occurrence of petroleum ; and as to the immediate north of tho anticline at Poututu there arc gas-springs and other indications of oil, and.also in tho district south of Hutchinson’s Range, Mr Brett was anxious to know whether an anticlinal arrangement of the strata existed in this district. In so far, then, tho anticipation has been realised. From the valley of tho Waikohu, on the 21st March, we returned and followed upwards the Waipaoa River to Mr Cooper’s station, at the junction of the Waingaromia with the Waipaoa, and the following day we followed the valley of the first-named stream and of its tributary, the Waitangi, past the site of the Pacific bore-hole, placed in the low grounds of the valley, south-east, some two miles from the oil-springs at the source of the Oil-spring Creek. The section of strata along the lower valley of the Waingaromia is not very clear, but on the whole the dip appears to be to the south-east at moderate angles. The rook exposed at and for some distance above the Pacific oil-bore is the grey sandy marls described as showing towards the east and on the south sido of the anticline along the Waikohu Valley. Higher up in the valley of the Waitangi the character of the rook changes, hard calcareous sandstones being more abundant in the shales, in which septarian concretions are of common occurrence. These latter beds are the true oilrocks of Waipiro Bay and the Waiapu Valley, and from Waitangi out-station may be traced south-west to the neighborhood of the oilsorincs.

From the Waitangi out-station we reacnea the oil-springs, situated on the watershed between Oil-spriag Creek (Mangataikapua being the Maori name of the stream} and the Waitangi, at a height of 1,400 feet above the ssa. The oil-springs are situated on the western side of the highest ridge of the range overlooking the Waitangi, about 150 lee* under the crest of the ridge, and are lodged in a shallow valley between that and a iov-ei ridge to the west, which bounds the valley of Oil-spring Creek on the eastern side of its opner part. These two ridges are connected by‘a saddle, and the oil-springs appear on this and to the south down a gentle declivity, along which the water flows in a small marshy creek-bed, and finds its way into the Waingaromia River. A third of a mile below the saddle the creek deepens, turns to the left, and in a sort of gorge breaks through the continuation of the higher eastern ridge to join the larger stream mentioned. The c-poer part near the saddle, between the two ridges described, has a breadth of from 10 to 12 chains, and the surface from the lower part of this are%>to the saddle at the source of the creek shows a succession of slips. How deeply these slips affect the strata it is not easv to determine, but as the disturbed ground is simply the sagging of tlis valley slope, slip by slip, it is probable the depth of the moving ground is not great, and the whole movement must be regarded as superficial. The slope of the western ridge overI looking Oil-spring Creek is affected in the same way, but here also the disturbanc: is of a superficial character. The crest of the western ridge is undoubtedly unmoved ground, and towards the north, -where this curves to the east to form the saddle between the northern and southern iloiv of the waters, the ground, except on the very saddle, is also solid. The saddle itself may have received some slips from ihe higher ridge to the east, but these are necessarily unimpoitant. The manifestations of oil at the surface display themselves in a series of holes, both natural and artificial, and oozings along the banks of the creek, and near the height of land where the western ridge tarns to the east, in this latter case apparently from solid rock. The amount of water, whether as flowing from deep-seated sources in the reek or simple drainage of the surface, was but little at the date of visit, and at no time can be great. There are seven pools, natural or artificial, filled with water and covered with oil to depths varying from 1 inch to -1 inch. The northern hole, with a surface area between two and three square yards, was set on fire without ascertaining the depth of floating oil, and this burned furiously for the space of a quarter of an hour, with a llamo 8 [t. or 10 ft. in height, and the elimination of much smoke. An artificial hole, 5 ft. by 2 ft. (5 in., showed oil to a depth of fully 8 in., and this also was set on fire, but did not make such a display as the hole further north. When all the oil had disappeared there remained as imcombustible matter on the surface of. the water a black substance showing the physical characteristics of oil, r.nd beneath that a yellow flocculent substance of a pale-yellow color, resembling yellow ochre, in a sluggish stream-i-The soil of tiro area over which these springs appear is of a peaty- character, and this to a considerable extent contains oil —a yellew substance resembling paraffin—and numerous grains of a siliceous mineral, probably pumice. With the object of reaching on to the country further west from the oil-springs, the ridges to the north-west were followed past the souree of Oil-spring Creek, beyond which we descended into a deep valley, in which lower oil-bearing rocks were seen, consisting of sandstones and shales, with spherical calcareous concretions, in character resembling those of Waipiro, beyond which broken hilly country was passed over, showing rocks of the same description, till, crossing the valley of another creek, the last ridge before reaching the main valley of the Waipaoa was reached. On the descent into this a calcareous coralline glauconite rock was observed, yielding blocks of considerable size. This was underlain by grey moderately soft sandstones, which continued into the low ground of Station Creek and the main valley of the Waipaoa River at Muir and Finlay’s station. The rocks along the lower part of Station Creek were examined, and a white siliceous rock was found —this being the lowest seen —overlain by sandstones and shales, with concretions similar to those underlying the glauconite limestone of the previous day’s observations, the whole dipping to the south-east. Following the main river (the Waipaoa) upwards, the dip of the rocks under the white siliceous rock was at first at a lower angle than on its south-east side, but at a distance of a mile the dip assumed its normal—an angle of 20 degrees to 25 degrees to the south-east. This was on the east side of the valley. On the west side of the valley the white rock was noted dipping at a considerable angle opposite the junction of Station Creek, and the beds appearing from beneath this, being much disturbed by surface slips, gave no indication of strike and dip for more than half a mile up the right bank of the river. At this distance above the junction of Station Creek an exposure in situ appeared, where a sharp anticline, with a syneline on its northern side, was displayed, beyond which broken slipped country again made its appearance on this bank of the river. Iu following the Waipaoa downwards through the gorge a sequence of soft grey sandstones, and sandy clays with harder bars of sandstone, were passed over. The dip of these was principally to the south-east, often to the south-west, and in the lower part of the gorge, where the dip was low, sometimes to the north-west. The average dip in the upper part of the gorge was 25 degrees to HO degrees, and in the lower part 5 degrees to 10 degrees. These rocks have a general resemblance to those of the Waikohu Valley, and differ only in the presence of a preponderance of the hard sandstone bars, which at places are 8 ft. to 10 ft. in thickness. The gorge of the river along which these rocks are displayed is narrow and deep, the country to the east being hilly, sometimes rugged, while on the right, or western, bank it is more plateau-like, and not so' broken in character. One mile before reaching the junction of the Mangatu River these rooks suddenly cease, and intensely dark glauconite rocks make their appearance; while a little further down the river white rocks, siliceous or calcareous, make their appearance, having a north-west dip. The juxtaposition hero of the higher and lower rocks of the series—strictly speaking, of the higher and middle rocks of the whole sequence—of necessity involves the presence of an unconformity or a line of fault. Down-stream these white rocks are again overlain by the soft sandstones and sandy clays so strongly developed in the gorge of the Waipaoa River, and these, dipping at a considerable angle, can be traced down the valley to the junction of the Waingaromia River, from which we set out. The appearance of the green and white rocks in the Waipaoa River, a little above the Minerva bore, and about a mile and a half above the junction of the Mangatu, implies—nay, proves—the presence of a fault dislocation or unconformity (which yet requires to be fully investigated), and shows that the tertiary rocks between the fault and Muir and Findlay’s station have an approximate thickness of 2,000 ft. This discordance must, therefore, be of considerable importance in a description of the geology of the district. The trend of this junction line is north-east and south-west, and, traced in the north-east direction, it crosses the hills intervening into the valley of Oil-spring Creek, and thence should be traceable past the near vicinity of the oil-springs into the valley of the Waitangi River, and how much further to the north-east cannot be determined. ' To the south-west it crosses the intervening hills into the valley of the Mangatu, where the white rocks in the same relationship are reported to be present by Mr William Cooper, whose acquaintance with the country is intimate. Vet further to the south-west the line of unconformable junction must cross the Urukokomoko Stream, within the valley of which Mr Cooper thinks the white rocks are also seen. Thence the distance to the point farthest west to which observations were carried in the valley of the Waikohu river is but some five railed - , where, if the white rocks were not observed, the glauconite calcareous coralline limestones were, and these, it has been shown, lie at no great distance above the white rooks. Oil and gassprings He along this line, or at no great distance from it, from Poutulu to the Waitangi, and the influence of the unconformity or fault-line on the appearance of these is evident.

Near to this line in the valley of the Waipaoa is the Minerva bore-hole, put down in search of petroleum. What influenced the promoters to place this bore where they did I cannot tell, but it was probably the near presence of the white rock, which is also not dislant from the oil-springs farther to the' north-east, and had it been located nearer, to the junction of the two formations, or carried to a greater depth, it might have been a more successful venture than it proved to be. Of boring at the oil-springs I have little trustworthy information. Both shafts and bores were put down to a moderate depth: to what depth I cannot exactly say, nor need this be to me, at least, a special matter for inquiry. It is enough to say that, whatever method was followed, and to whatever depth these attained, none of them were situated on solid ground, while sites on solid ground might have been obtained in the nearneighborhood, and at bnt a little greater elevation; bnt; not knowiog what gnided the selection of these - sites, I may well refrain from commenting thereon. The South Pacific bore, in the valley of the Waingaromia Biver, was clearly a plunge in the -dark more so than that of the Minerva in the Waipaoa Valley,