NATURE NOTES.

New Zealand Herald, Volume LXIX, Issue 21118, 27 February 1932, Page 1 (Supplement)

NATURE NOTES.

BY J. DRUMMOND, F.L.S., F.Z.S,

PETRIFIED FOREST.

The remarkable petrified forest exposed by the sea on the strand at Curio Bay, Waikawa, Southland, seems to show that in the Jurassic Period, in which they grew, there were lofty trees. An American writer stated that the Jurassic Period had nothing in height like some trees of modern times, but at Curio Bay, standing erect as when they were living plants, are 6tumps two feet in diameter. Two hundred stems, varying from that diameter down to two inches and one inch, may be counted on the beach. Many of thern are from one foot to six feet high. Kocky ledges are thickly strewn with the prostrate trunks and limbs more than fifty feet long. One trunk measured more than 100 ft. These flinty relics of an ancient forest resist the attacks of the sea much better than they are resisted l>y the encircling rock, and some trunks pass up through beds of shale and sandstone, and stand out boldly on a cliff, defying the raging and swelling of the sea.

The Jurassic Period was a division of the Mesozoic Era, the Era of Middle Life, Few fossil forests of the Mesozoic Era are known. The forest at Curio Bay is the most remarkable of them all. The big trees, chiefly comprising the old pine forests, apparently, were members of the Araucarian group, to which the monkeypuzzle and the Norfolk Island pine belong. At least one species of the Curio Bay conifers grew abundantly in other parts of New Zealand in Jurassic days. Later, it enlarged the borders of its tent, taking in India and part of Antarctica. At Curio Bay, these trees stood in stately majesty above dense thickets of cycads, which do not grow in New Zealand now. They reseipble palms, and in a few Jurassic forms they were crowned with flowers five inches in diameter.

At the feet of the forest trees there were masses of ferns. Among these was a species noted as the great weed of the Mesozoic Era, Cladophlebis Australis. It was the commonest plant in Jurassic New Zealand. With amazing vigour, it, like the bracken fern of these times, flourished in many widely separated parts of the world, leaving in Mesozoic rocks all over tie Southern Hemisphere abundant evidence of its success. The sizes of the big trees at Curio Bay show that the Jurassic climate there was mild. Those climatic conditions were almost the same as the conditions in our modern temperate zones. Fossils in other countries speak of a mild Jurassic climate all over the world.

The Jurassic Period saw stupendous elevation of the land. Where water stood before, dry land appeared. New Zealand, Tasmania and Australia, and the great continents were converted into vast land areas. This gave terrestrial species of plants opportunities to spread widely, more widely, it is believed, than plants, extinct or livingj _ spread at any _other_ tirngj „ typical Jurassic vegetation was world-wide. Yet it was not very rich in species. Only about 500 are known. Cycads were the most abundant and most characteristic. For this reason, the Jurassic is called the " Age of Cycads." The ginkgo, or maidenhair tree, was abundant and widely distributed. It probably grew extensively in New Zealand then, but the only fossil record of its presence is at Mount Potts, west of Christchurch; and this plant should be described as ginkgo-like. In outline, its leaf was like the typical ginkgo's, but was cut into many 6trips.

In spite of its former greatness, the ginkgo is represented in the world now by a single species, a native of China and Japan, but introduced into many a garden as an ornament. It thrives well in New Zealand gardens. Its pyramidal shape and its light green broad, flat leaves with forking veins like veins on the leaves of the maiden-hair fern, are much admired. The species has lived through the ages so little changed that it is difficult, perhaps impossible, to find any essential difference between leaves of the living plant and of the ancient plant.

The name Jurassic was given to this period because rocks that record its events are highly developed in the Jura Mountains, between France and Switzerland. Muds and sands of Jurassic estuaries are very rich in fossil plants. Sediment was laid down on the floors of Jurassic seas evenly and steadily. The world's plant covering was uniform. Some groups of plants flourished more abundantly in some parts than in other parts. Some species, although common in wide areas, were not cosmopolitan, but the knowledge available leads to the conclusion that the Jurassic. vegetation was less diversified than the vegetation at any other period of geological history.

The main difference between the Jurassic vegetation and present vegetation is Iho absence then of plants dominant now. Imagining that he was walking near a Jurassic estuary, Professor A. C. Seward, of London, saw conifers dominating tho forest; river banks hidden under a tangled riot of luxuriant ferns; groups of liorsetails spreading a green mist over flat stretches of sand. He was impressed with the absence of broad-leaved trees festooned with rope-like climbers, their branches lifting up to the sujibght clusters of humbler flowering plants. Ho felt that ho had wandered into a country where tho ground was monopolised by conifers, ferns, and cycads, to the exclusion apparently of flowering plants.

In dealing with geological time, allowance must be made for its stupendousness. People must think in millenniums, not in years or in centuries. This should bo borne in mind when it is stated that, on tho measurement of time, based on radioactivity, 155,000.000 years have passed sinco the Jurassic Period began. It covered 35,000,000 years, and then merged into the Cretaceous Period. Fossils show that Jurassic sens swarmed with ferocious creatures, sponges and corals were plentiful, and there crawled on the floors of the seas, or swam through tho water, snails, crustaceans, cuttlefish and squids.

While sonic botanists call the Jurassic Period tho " Age of Cycads," some zoologists call it tho " Ago of Ammonites," on account of the development at that time of a numerous and plentiful group of shellfishes with coiled shells like the horns of Jupiter Amnion. They wcro so plentiful in New Zealand seas and in every other Jurassic sea that the cause of their expiration is one of the world's mysteries. The earliest known birds lived in Jurassic forests. In the mud of Jurassic estuaries in other countries there have been found tho remains of many insects, including flics, beetles, moths and butterflies. It has been suggested that these insects were blown seaward by strong winds, fell on the surface, were drowned, to the bottom, and were preserved impcrishably in the sand or mud.