NATURE NOTES.

New Zealand Herald, Volume LXIII, Issue 19412, 21 August 1926, Page 1 (Supplement)

NATURE NOTES.

WRITTEN IN THE ROCKS. BY J. DRUMMOND, F.L.S., F.Z.S. From the horizontal, or almost horizontal, form in which sedimentary rocks originate they may be altered until they tilt all angles. Some of them now stand up on end. Others have been completely overturned. The folding that produces this is the result of long and stupendous pressure. Rocks yield to pressure without. breaking, in the same way as cloth may be folded. The folds in rocks sometimes are so small that several could be included in a piece no larger than a man's hand; sometimes they change the face of a whole district. Rocks often fold into the form of arches; others fold into troughs. These natural arches are anticlines, and troughs are synclines.

Rocks in an upland which has Kawhia and Raglan as its chief centres of population, and along which tho principal road between Auckland and Taranaki ran before the Mam Trunk Railway was opened, are arranged in a gigantic trough twenty miles wide It is complete only south of the Kawhia depression; northward, its great western wing was depressed below sea-level in Tertiary times, when Nature traced some of New Zealand's present features. Tho trough is traversed by many faults. These havo broken the rocks into largo blocks. The main mass of the upland is formed of rocks laid down in the Mesozoic Era, which came after tho Palteozoic, and before the Tertiary or Cainozoic, the era that immediately preceded the ono in which we live.

The upland extends along the coast as a distorted plateau, deeply dissected. An ancient dilapidated volcano, Mount Pirongia, rises from it for 3150 ft. in the south, and a mighty corner buttress, Mount Karioi, rises 2420 ft. south of Raglan Harbour. In the north-west corner of the district there is an ancient surface that rises from sea-level near the coast to 1100 ft. Raglan Harbour was formed by tho sea invading the lower part of a branching river-valley. Kawhia, Aoteb and Whaingaroa Harbours are the result of an invasion by the sea of valleys eroded by streams Remnants of sea-terraces along tho shore show that, although tho land there has sunk, to admit the sea, it once was lower even than it is now. A bench, from 190 ft. to 250 ft: high, up to four chains' wide, backed by an old seacliff, runs for half a mile along the coast. North of Aotea Harbour there are wellmarked terraces about 200 ft. high. Tho flat tops of many high ridges indicate ancient shores. A lowland, extending for about thirteen miles from Waikorea Stream to Raglan Harbour, probably originated when the shore was from 500 ft. to 600 ft. higher than it is now. Most of the hot springs in that part issuo from Mesozoic rocks.

Every lake, in every country, like every individual and every nation, has youth, maturity, old age, decay and death, and is under one of the greatest laws of Nature, the struggle for existence. The life-histories of lakes in tho basins of the Waikato River, which drains the eastern side of tho upland, are not less interesting than the life-history of the historical river itself. Lakes in the middle basin of the Waikato have died sinco settlement began. The bed of Lake Rotorangi, six miles south-south-east of Cambridge, is now dry land. Tho bed of Round Lake, two miles south-east of Ohaupo, is dry except after rain. The area of Lake Hamilton has been reduced by the draining of swamps to the west. The Waikato carrying sand and silt, has dammed the Mangawara River, until its lower course, for three miles, is a narrow winding lake. Eight lakes in the lower basin of the Waikato, and east of the river, have several characters in common. AH are very shallow; their surfaces are slightly above the normal level of tho river; their oulets are across wide, swampy fiats of the present flcfod-plain; their flood-plains pass gently below the surfaces of the water. Encroaching sanddunes, blocking small streams, have formed ponds near Raglan North Head and north of Kawhia. Parangi, a pond near Kawhia, 150 ft. above sea-level, lies among pld fixed sand-dunes, cemented with iron oxide, but loose sand is rapidly encroaching on it. Many ponds and lakes in the middle basin of the_ Waikato probably are remnants of Hikes that once were much more extensive. The lakes of the Waikato, one of the most noticeable landscape features'of that part, seem to be particularly ephemeral—this word may be used with strict propriety when a thousand years are as a day—and thoy may he merely an incident in the dis-, trict's geological history. With ponds, swamps, lakes, and rivers all changing and all passing through their cycles, that part of New Zealand is an open book in winch he who runs may read chapters in tho Dominion's history.

During Eafly Tertiary times the site of the Lower Waikato basin was loveland, probably the wide lower valley of a river. A slight depression of the land allowed swamps to extend over the lowland. The swamp vegetation was most luxuriant in the hollows of tho old land. Layers of silt and mud were spread over the swamps. , These deposits were soon covered by vegetation in their turn. Then sediment in large quantities was deposited on the great swamp. Vegatation overgrew it also; and that vegetation forms tho upper coal-seam at Huntly and Rotpwaro. Depression continuing, the swamp was covered by the silts and muds that now form grey and brownish clavstones which over-lie the coal. The Glen Massoy coal is believed to have been formed in the same wide valley in which the Huntly coals accumulated, but it was at a later period, when the depression of tho land was more advanced, and after the sea had penetrated further inland and the Huntly coals had been all covered with mud. Between South Head and Kawllia and Te Mairi, in layers of sandstone, petrified.trunks and stumps of trees stand where they grow.

The sable seas of the Mesozoic E:ra were characterised by ''a great development of molluscan life. Their chambered division was represented by ammonites, and the cuttlefishes by belemnites. Both those molluscs, now extinct, have left their remains in many parts of the world to help in reading the history of thoir times. Both ammonites and belemnites are scattered over the Huntly-Kawhia district, with the shells of other Mesozoic magnates that were their contemporaries. All this, and more also, is set out by Dr. J. Henderson and Mr. L. I. Grange in Bulletin No. 28 of the New Zealand Geological Survey, recently issued from the Government Printing Office. This is the latest of an admirable series of geological works published by the Survey. An examination of the coal-beds near Huntly was the basis of the bulletin. The authors extended their researches to a comprehensive geological survey. The district contains no precious metals, but it is rich in brown coal, limestone and clays; and its geological history, as sketched in this bulletin, is more fascinating than any human history. In comparison with the geology of that district, with its ups and downs, the migrations of creatures that peopled it long ago, the advance and retreat of the sea, and outbursts of volcanic activity, the strife of powers and principalities sinks, into the limbo of insignificance.