“THE LAND WHERE WE LIVE.”

Manawatu Herald, Volume LI, Issue 4540, 6 December 1930, Page 3

“THE LAND WHERE WE LIVE.”

■INTERESTING sketch of FORMATION OF MANAWATU.

■Mr. R. Edwards, of Palmerston 'North, was the speaker at Thursday’s Lunch iCluh meeting and his subject, “The Land Where We Live,” proved most interesting. Mr. Edwards, who was one of the editors of the report on the New Zealand Institute of Scientists Congress held in Palmerston North in 1021 was congratulated on a paper on the same subject which he read at the (Congress. The area dealt witli by Mr. Edwards was the flat land lying southwards of the mouth of the Rangitiikei river, extending between the ocean and the western flanks of the Tararua Ranges, to a point opposite the southern end of Kapi'ti Island. The geological problem, he said, was how did this district come inexistence? This problem involved careful observations of the surface, and an accurate knowledge of (lie stratum deep down into the earth. Perhaps the most difficult thing we experience when we come into contact with geolo-

gical teaching' for the itirst time, was the great demand made upon the imagination, said the speaker. In dealing with a part of the surface referred to, viz., land lying

between the Manawatu River ami

the flanks of the ranges, more particularly the Ohotuiti and the Alakerua Swamps, away buck through the vista of the dim past we see these swamps—and a considerable area to the westward of them — heavily timbered. Imagine for the time being a beautiful forest with all its pretty flowering shrubs, climbing plants, and labyrinths where the beautiful New Zealand birds lived in peace and happiness. Such, undoubtedly, was the state of the surface of.this area mice, but at the present time, how different. The surface is covered mostly with flax, raupo, tutu and the usual swamp growths, small patches of light bush, and small lagoons. The problem is, how did this change come about, and from what cause? In the centre of the Ohotuiti swamp there is the ,bed of a drained lagoon, and the surface of a dead forest is plainly seen. The question is, how did this forest disappear about six feet below the surface of the water under normal conditions, and about 13 feet or more below a high flood level? The bed of this lagoon is now only about 1 foot above ordinary spring ‘tide level. It is quite certain that a forest would not grow at such a level, and at one time it must have been greatly above sea level. The whole district referred to was a great deltoid flat, amongst a number of bifurcating channels, viz., the Rangitiikei, Oroua, Poliangina, Manawatu, Tokomaru, Horowhenua, Ohau, Otaki and the' Waikanae rivers, which have all contributed to (produce this district from the slopes of the Tararua and Rnahine Ranges, continuously away ibac'k to a glacial period. At one time the ocean washed against the Western flanks of the Tararua Ranges, which was described as the primeval formation. Our delta district certainly rested upon the primeval formation dipping down under the ocean, and the plain cause of the subsidence of the delta formation

(which 'accounted for the submerged forests) was the gradual set-

{lenient and consolidation of the river deposits. By continuous slipping down the general formation had now reached a safe angle of repose peculiar to such formations, the toe of which was miles under the sea, resting on the floor of the ocean. ■Mr.'Edwards said he had not got records of a hydrographic survey of the ocean on the coast, but it was possibly about 500 to 000 feet deep, extending to a depth of

three miles in the direction o£ Australia. In order to avoid taxing yoiu* imagination too much, and pushing through the mists of geological history, said the speaker, I have compiled the following' records '■ which are an accurate description of the stratum below the district outlined, and thus we see beyond — dimly through the mists of the past, the Story of the formation of tliis delta. (1) —Foxton, triangle Main St., - observations made from bore sunk •to a depth of 528 feet, and iindings may Ibe taken' as approximately •correct within a mile radius of that site: —To a depth of 20 feet common grey and black sand, followed by a small seam of peat above a seam of metal which extends—mixed with coarse black sand —to a depth of 50 feet. • From 50 feet to 150 feet line sand mixed with sea shells. From 150 feet to 180 feet stieiky blue clay. From 180 feet to 254 feet fairly coarse gravel. This is one of the best wa-ter-bearing strata, proibably the same seam of metal which extends towards the ranges through the Moutoa as far as the Manawatu itiver. At a depth of 254 feet there is a seam of black peat 3 feet in thickness; from 257 feet to 414 feet tine sand; from 414 feet to 458 feet white clay—commonly known as papa; from 458 feet to 528 feet coarse sand and fine gravel, the water from this stratum rising 2ft. Bin. above the surface of the ground, or 10 feet higher than the flow at a depth of 180 . feet to 254 feet. (2) —Moutoa: —From about 50 artesian wells sunk I have gleaned the following facts: —On the av-

erage there is first a depth of 3ft. of soil, mostly alluvial deposit ' followed i>y a previous surface

formation of soil mixed with decayed vegetation, flax roots and timber; from 5 feet to 20 feet sticky blue clay; from 20 feet to 110 feet fine soft gray sand, and quite a large quantity of sea shells. Then follows an average thickness of .10 feet of elay, followed by a cavity about 3 feet through. A considerable pressure of gas is found at this depth, and I believe it might bo possible to utilize this gas for fuel and lighting purposes. Under this stratum there is another seam of blue elay about. 20 feet thick, followed by metal at 140 feet from which some of the finest flows of water in New Zealand are obtained. (3). —Part of the Makerim Swamp nearest the river is very similar in formation to the Moutoa. The portion of swamp exlending from Ivoputaroa- lo Tokomaru lying nearest the range, and also comprising the first terrace, contains the following, viz.:— ■ A depth of 85 feet on the swamp, and 180 feet on the terrace of red sandstone, mixed with \ellow elay followed by 4 feet of black pent, which is almost as solid and hard as coal, then follows an average depth of 120 feet of black sand, then usually another •1 feet of hard peat followed by coarse black sand or gravel. Enormous Hows of beautiful water (almost free from minerals) arc obtained from this stratum, as example 1; 2-ineh bore near Makerun school at 275 feet deep rising 54 feet above the surface, and at. the point, at Koputaroa it. runs 58 feet above the surface.

Referring to the various strata commencing at Main Street, Foxton, at, the surface we have line sand followed by small seams of peat (original swamps), at about 20 feet, again at 254 feet another seam of pent 3 feet thick; at 528 feet the greatest depth, line gravel, 'flms we find that a. swamp once green which was now approximately 230 feet below the sea level. Moutoa 'District: —At 120 feet down cavities are frequently met with which are probably formed bv decaying timber and vegetation. At a depth of 123 feet logs, varying from 1 foot to 3 feet in diameter are found. Mr. Edwards said he was of the opinion • that this timber did not grow at. this point, but that this level was once the sea beach, and the logs, after having been washed down the rivers, were cast up on the beach from the ocean exactly in the same manner as we see logs deposited on the ocean beach at the present day. This level is approximately 100 feet below the ■>ea level.

At a point, about 00 chains along Maxwell’s Line, and east of the railway line, about 30 years ago the surfaco was clothed in hush, hut has been felled for about 14 years. Excavation 12 feet deep revealed a submerged forest.

The stratum at Palmerston N. was of course an alluvium, but differing somewhat in character to the deposits nearer the coast, and contained a large quantity of metal brought through the gorge by the Manawatu River, and also down the Pohangina River. As the velocity of these flows decreased as they spread out on the flat country the metal was thus deposited.

Donbtless the settlement and consolidation of the alluvium, in addition to the action of the water, had been considerably accelerated by earthquakes, indeed, when if. was considered that the great forests referred to apparently died at, or at about the same time, one was forced to take this view. Mr. Edwards also touched 'on the Palmerston North and Foxton water supplies. The artesian supply at Foxton, he said, was not (piite as good as that of Palmerston North, due to the fact that at Palmerston North the water was filtered through metal from the slopes of the ranges while at Foxlon it percolated through old swamp lands which naturally did not tend to purify it to the same -extent as .that of Palmerston N. The “head” or pressure at Palmerston. North, was also better and this was due 'to the fact that a licit, of sand packed almost to the consistency of concrete surrounded 'the city which formed a greater resistance to the water than the shingle did. Consequently when the flow was tapped the water, backed up by the sand belt, provided with an easy outlet came up under great pressure. Complaints had been heard regarding the hardness of the (Foxton water, but Mr. Edwards had no doubt that this could easily he overcome if it was dealt with on the proper lines. The speaker also referred to the fact that all the rivers along this coast, were making south. The explanation for this, he said, as advanced by one of New Zealand’s scientists, was that the prevailing winds on this coast were from the south-west; and they blew sand into the rivers. One would naturally think that this would cause the rivers to make north, but the effect was the very opposite. In addition to this, the rotation of the earth had the effect of causing a slight pressure on the southern hanks as explained by Ferrills Law. This was considered farfetched by some but nevertheless the pressure was constantly there und must have some effect with the passage of year's. At the conclusion of his address Mr. Edwards was accorded a hearty vote of ‘thanks on the motion of Messrs G. F. Smith and Rev. W. H. Walton.