NATURALISTS’ FIELD CLUB

Evening Star, Issue 23696, 2 October 1940, Page 12

NATURALISTS’ FIELD CLUB

DESERT AREAS Mr Xily’s lecture entitled ‘ Terra Desorta proved full of interest to members of the above club. It included not only tbe hot, dry lands usually associated with the term desert, but also all uninhabitable portions of the earth. Usually desert meant that conditions were too hot and too dry, but too much water and too great a degree of void could also render a region unlit for habitation. Instances of this were cited in the desert areas of the Arctic, where the scant vegetation could not support inhabitants, and only where the reindeer could survive to supply man’s many needs. In tho hot, moist regions of South America vegetable life was so rampant and animal life so abundant that, rnau could not prevail against it, and so these regions, too, were uninhabitable. The dry deserts were areas of high atmospheric pressure, and thus winds blew from them and not to them, and so water was kept out. They were usually far from the sea and surrounded by mountains which precipitated moisture from outside, and so kept them dry. These desert areas formed two belts, tlic. Sahara, Arabian, Persian, Indian, and Mongolian forming one bolt, and to the south the Kalahari, Australian, and South American Deserts formed another belt. In temperate regions deserts were usually on high plateaux, as in tho Gobi and Colorado Deserts. In hot, dry areas the scanty vegetation was especially adapted to withstand the arid conditions. Plants were coated with a waxy substance, they hung their leaves endgewisc to tho sun, they protected themselves with spines and thorns, they grew very long roots, or they had specially adapted vascular structures. The animals, too, were suited to their environment. They were coloured to match the sand, had broad feet for walking, and wore capable of storing water. The camel was a typical desert animal. The population of these areas was of two types, the lent dwellers who lived a wandering life and those who lived in slono houses near the oases. Their life gave them plenty of time for meditation, ami the clear night skies offered opportunity for the study and observation of the stars. Thus it was that many of the great religions of the world had had their origin in desert countries, and the earliest knowledge of astronomy had come from desert dwellers. It was known that these regions had once been cultivated and inhabited, and many wore the speculations to account for their subsequent desiccation. It was thought that at the time these countries wore at. tlic height of their development the earth was just recovering from the glacial epoch. Tho European counlrios were then very wet and swampy and in a very backward state of development. It was much drier in the south and civilisation more advanced. When the glaciers retreated and melted the oceans became deeper and the land rose higher. The great Sahara Desert was characterised by crosccnt-shapcd sand dunes, or barchans, which moved slowly across the desert, travelling before the prevailing wind. When the wind was not very strong the characteristic crescent shape was preserved, but with a stronger wind the barchans merged to form an irregular-shaped barrier. Where gales blew the dunes were cut into long lines running parallel with the direction of the wind. Tho prevailing wind was from the north-cast, so that tho sand started close to Egypt and travelled right across the desert to tbo Atlantic, and then was blown out to sea. For many miles along the Atlantic coast liio sea was shallowed by tho huge quantities of sand which had been blown from the Sahara Desert, As ; rocks decomposed salts were formed, which in damp regions would be washed away, but in desert regions as the scant moisture dried up the salts formed white powder and crystals on the surface. This process was sometimes so extensive that whole areas were covered with deposits of sodium carbonate, sodium bicarbonate, borax, or sodium sulphate. These had considerable economic value, but wore so unpleasant to travel through that they were avoided wherever possible. Salt lakes were numerous m areas that had no outlet, the salinity of the water increasing with evaporation. If the lake dried up altogether often deep salt deposits would be left. The Dead Sea was not an ordinary salt lake, for it was believed that the Jordon and other streams feeding it were nob merely bringing the usual salts carried by all rivers, but were dissolving salts loft by former salinas. The brilliant colours sometimes seen iu the desert were formed when salts brought to the surface by capillarity reacted with the rocks, there Iron formed a bright red coating and manganese a dark coating known as desert varnish. Although Nature was responsible for most of the desert areas, man created deserts when he removed tbe vegetation, as was evidenced in the great desert regions of China, where all trees had been cut down, resulting in the utter destruction of stretches of once fertile country. Mr Williams moved a. hearty vote of thanks to Mr Tily for his interesting address. EXHIBITS. Miss Finlayson sent a specimen of clematis quadribracteolata somewhat resembling C. marata, but differing from it in having purple flowers instead of greenish, and blooming a month earlier. It has a more beautiful fruit and is not so sweetly scented. Miss Cartwright showed an interesting exhibit of earth stars. SATURDAY’S OUTING. A small party walked from Abbotsford to the sand dunes of Green Island Beach, midway between Black Head and the Kaikorai estuary. Many nests, both new and old, were observed in the budding hawthorn hedges. Turning to the left from the main Brighton road, the party followed a track leading down past a grove of ngaio trees through lupine, marram grass, and tho native pingao to wide desertlike stretches of sand, under which the water of the streams from the hills above disappears, only to reappear curiously in miniature canyons and waterfalls near tho beach. There wore few shells on the beach, and the only seaweed noticed was the yellow lather-liko one with long tapering bladders. On a damp patch of sand where creek water disappeared from sight was a bed of liverwort with pretty lavender colouring at the margins. An interesting, sight was that of 14 Australian black swans flying northward over Green Island in regular V formation.