My Science School

       Flint is one of the various forms of silica, which is among the common materials making up the largest part of rocks. Some other forms of silica are quartz, opal, chalcedony, agate, jasper and onyx. Flint (essentially, silica with some water, a little lime, oxide of iron and, occasionally, carbon) can be grey, grayish-white, smoke-brown, brownish-black, red or yellow. It occurs as layers in other sedimentary rocks.

       Because it flakes and can easily be chipped into a sharp cutting edge, flint was used by prehistoric man to make axe heads, arrow heads, knives and other such sharp-edged implements.

        The study of implements from the Paleolithic, or Old Stone Age, and the Neolithic, or new Stone Age, has helped us understand how people lived them.

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     Stalactites are the stony deposits hanging like icicles from the roofs of caves. Stalagmites are similar deposits rising in columns and cones from the caves’ floors.

     Caves occur chiefly in limestone and chalk formations, because water dissolves these rocks. The river Lesse, for example, in its passage through the caves of Han, in Belgium, has been estimated to dissolve some five tons of limestone in a day. It is redeposited as carbonate which builds up the stalactites and stalagmites.

      The seepage of water down the cave walls and through the roof produces constant dripping and evaporation. Stone icicles form on the cave roof, slowly growing with the addition of successive layers of calcium carbonate. The word “stalactite” comes from the Greek and means “drop by drop”. There is, too, a general term “dripstone” which is used to cover all formations.

    Stalactites are at first hollow, for the depositing of the carbonate is fastest at the outer ring of the water drop. As the evaporating water deposits its mineral matter, the cavity slowly fills up and the stalactite becomes solid. When water trickles out of a narrow cleft in the roof, instead of a small hole, a hanging curtain of stone will form in place of a conical stalactite.

     If the water flows so quickly that it splashes on the floor of the cave, it deposits its calcium carbonate there and small cones and domes of stone called stalagmites begin to rise. These may grow up to join the stalactites above and from single columns. Some cave floors are covered with stalagmites. They may grow so high that they block the cave entrance.

   The tallest known stalagmite, measuring about 98 feet high, is located at Lozere, France, in the Aren Armand cave.

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          The pebbles that are to be found on a beach are invariably round and smooth owing to the constant battering they have received from the sea.

          Originally pebbles were part of much larger rocks, but various natural phenomena such as earth-quakes and volcanoes, have gradually broken them down. Caught in the movement of the sea, and constantly rubbed against other hard materials, the pebbles finally lose their irregularities and present a smooth round surface.

          Many of the rocks of today will be pebbles in thousands of years time, and many of today’s pebbles will eventually be turned into sand by the constant, wearing action of the sea.

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     The Pillars of Hercules are on either side of the Strait of Gibraltar. The legendary Greek hero Hercules was said to have erected the Pillars on a journey to capture the Oxen of Geryon, a monster with three bodies who lived on an Atlantic island. Passing out of the Mediterranean he threw up the rocks on either side of the strait of Gibraltar. They were the Rock of Gibraltar and the headland on the Moroccan side.

      Hercules’ journey was one of the 12 labours that the son of Zeus had been set by Eurystheus, king of Tiryns, whose servant he had become. One of the most famous of these labours was the cleansing of the Augean stables. So in-numerable were the herds of cattle that used these stables that, as they returned from pasture, they seemed to reach endlessly across the plain. Their stables were heaped high with manure and had not been cleaned for years. Hercules diverted the Rivers Alpheus and Pereus through them, and completed the task in one day.

      For his last labour he braved the underworld to capture Cerberus, its three-headed watchdog.

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      A national park is an area where natural scenery and wildlife is protected by law to preserve them for future generations. It is only recently that man has realized that he must make a positive effort if many species of wildlife and areas of great beauty are  not to disappear forever.

      There are many kinds of areas of conservation and their central priorities may differ slightly. In the U.S.A., a national park such as Yellowstone safeguards natural features and wildlife in a way that will contribute to public enjoyment. In Africa generally, as in the Amboseli Game Reserve, the chief purpose is the preservation of the great herds of animals which once roamed the country.

     National parks depend on tourists for revenue but the animals must remain unmolested. To solve the problem many parks restrict visitors’ movements by setting aside areas for hotels, restaurants and parking places and providing a limited number of roads through the park. National parks may be small or large, privately. Or government owned.

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    An atoll or coral reef begins to form when tiny marine animals called coral polyps attach themselves to rocks on the sea bed. the reef, which eventually takes the shape of a ring or horseshoe enclosing a lagoon, is made up of the lime-based skeletons of in-numerable polyps.

    After building skeletons round themselves, coral polyps produce new polyps, which in turn surround themselves with skeletons. The young polyps remain attached to the parents so that succeeding generations combine to produce a great mass of coral.

    Atolls occur only in shallow water where the temperature is over 65 f (18.3 C). They are found in the West Indies, the Indian Ocean, along the coast of Brazil and, notably, in the pacific. North-east of Australia huge reefs have formed and some atolls may stretch 40 miles in diameter and more than a thousand feet in depth.

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         A Spanish explorer, Fernando de Soto (1496-1542) was the first European encounters the wide and muddy waters of the Mississippi river. A veteran of Pizarro’s conquest of Peru, he was governor of Cuba when in May 1539 he set out with 600 men on an expedition in search of gold. By 1541 his wanderings had led him to the Mississippi but a year later he died of fever on its banks and was buried in the river at night to conceal his death from the Indians.

       The next white explorers were two Frenchmen, father Jacques Marquette, a Jesuit missionary, and Louis Jolliet, a trader, who in 1673 descended the Mississippi as far south as the Arkansas River.

       Their trip inspired another Frenchman Rene Robert Cavalier, Sieur de La Salle, to complete the exploration. He obtained permission for the expedition from King Louis XIV of France and in 1682 travelled down first the Ohio and then the Mississippi to its mouth in the Gulf of Mexico. He named the new territory he had explored Louisiana in honour of his sovereign, but was assassinated while trying to establish a colony.

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       One of the most convincing explanations of why the continents drifted apart is that the earth expanded considerably after its creation. This theory can illustrate by imagining the earth as a balloon and the continents as pieces of paper stuck on the outside. As the balloon is blown up the pieces of paper will grow farther apart.

      Other theories suggest that the continents only appeared to drift apart because masses of land were drowned under volcanic waters. But it has been demonstrated that land masses are, in fact, made to drift, by the heat generated from the earth’s interior and from earthquakes.

       Probably a combination of various theories may be necessary to provide a complete explanation.

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        The Heligoland Bight is an arm of the North Sea extending south and east of the red sandstone island of Heligoland. Heligoland is a small remote island of the German north Frisian group lying in the North Sea between the coast of Schleswig-Holstein and the estuaries of the Jade, Weser and Elbe. It is 5,249 feet long and 1,640 feet wide at its broadest point.

          In 1807 Heligoland was a Danish possession but it was seized by the English in 1814 and given to Germany in 1890. Before 1914 Germany developed it as a great naval base with an extensive harbor in the south-east. There was a network of underground fortifications and coastal batteries and it was known as the “Gibraltar of the north Sea”. The Heligoland Bight became famous as the scene of a naval battle between the British and the Germans on August 28th, 1914.

Heligoland became a strong hold again under the Nazis and the capital town of Heligoland was destroyed by Allied bombers. In 1947 the whole character of the island was changed by the destruction of the fortifications.

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      Earthquakes occur mainly in the regions of the earth where mountains are being formed, and where the earth’s crust is under strain.

      Some mountains are formed of great thickness of folded sedimentary rock laid down beneath the sea. Heat currents deep within the earth are thought to suck down sections of the undersea crust and so produce great trenches thousands of feet deep. When the heat currents die away the material forming the bottom of the trench begins to rise because it is lighter in weight. Eventually it is thrust up as a mountain range.

    This is never a smooth process but is accompanied by great friction and heat, as well as by rending and shearing and tearing of deep underground rocks connected with mountain formation cause earthquakes. Even small underground movements may produce violent surface shocks. The great Tokyo earthquake of 1923 which is believed to have killed 25 million people was caused by the twisting of a section of the earth’s crust in Sagami Bay.

     As might be expected, ocean trenches are the seat of a great many earthquakes, for there the earth’s crust is in an unstable sate. Indeed all the deep earthquakes those taking place more than 160 miles below the surface-originate around the Pacific trenches. About 90% of the intermediate earthquake (30 to 160 miles deep) also originates there, as do 40% of the shallow earthquakes (less than 30 miles deep).

      Some shallow and intermediate earthquakes are caused by volcanoes or by a slight shifting of layers of rock at a weak place or “fault” on the earth’s surface. One of the most famous and widely publicized of these is the San Andreas Fault on which San Francisco is built.

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      Locks are watertight chambers which enable boats to ascend or descend to different levels in a canal or river.

      The lock is usually rectangular in shape with gates at either end. If a boat has to go to a higher level it enters through the bottom or downstream gates of the lock, which are then closed. The water level in the lock is raised to that of the higher part of the canal by filling from the upper level and the upstream gates are opened to let the boat out. The opposite procedure takes place when a boat needs to descend.

      Locks used to be made of timber, brick or stone, but now concentrate and steel piling are more usual. Originally the chamber was filled or emptied by sluices in the gates. Now a day, as locks become bigger, these are often replaced by conduits or pipes running the whole length of the structure, with offshoot pipes running into the lock to give an even discharge of water. Old locks may be manually operated but new ones are worked by hydraulic power.

      Locks vary tremendously in size from about 123 by 17 feet (38 by 5 meters) on small canals to the giant locks on the Mississippi River in America, which are 1,200 by 110feet (366 by 33.5 meters).

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       Artesian wells are those from which water flows freely. These wells are man-made and are created by boring into the rock to a channel that is lower than the water source.

      The resulting artesian well has the advantage over vertical wells of not requiring a pump. The water will pour out naturally without the aid of any mechanism until the well runs dry. For this reason artesian wells, although often several hundred feet deep, may be only a few inches wide. This prevents undue loss of water.

    The term “artesian well” is derived from Artesium, the ancient name for Artois in Northern France, where a famous free-flowing well was excavated early in the 12th century.

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            The sextant was invented in England in 1732 by John Hadley. Hadley’s instrument is used mainly at sea to determine a ship’s latitude, or distance from the equator. Its invention laid the foundation of modern navigation with the aid of the sun and stars.

              The instrument is so called because it is equipped with an arc which is usually one-sixth of a circle, or 600. It measures the angle of the sun’s or a star’s altitude above the horizon. As this angle varies with the distance from the equator, the information obtained helps the navigator to calculate his position. All he needs in addition is the time, the date and the longitude which can be found by comparing local time with the time at Greenwich.

         To operate the sextant, the navigator looks through its small telescope straight at the horizon. At the same time, an image of the sun is reflected by mirrors into the user’s field of vision. When the sun is made to appear exactly on the horizon, the arm which moves the mirrors gives the required measurements to calculate the ship’s position.

       The handling of a sextant is generally to as “shooting the sun”.

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      The name dust bowl was given to the man-made desert in the central United States in the 1930s. There dust storms blew which were as severe as any on record. One storm in 1933 was traced for 1,300 miles to northern New York.

      For the origin of the Dust Bowl we must go back to the late 1800s when homesteaders were advancing relentlessly towards the west and planting their crops in the short-grass country, land known previously as the American desert. The farmers brought with them strains of hard winter wheat that were resistant to drought, disease and insects. They ploughed into the thin grassland and sowed the seeds both of wheat and tragedy.

      The states involved were western Texas, Oklahoma, Kansas, Nebraska and North and South Dakota to the pacific coast. Wheat was the principle crop. Dry farming techniques were developed. These enabled farmers to conserve the meager moisture in the soil by a process of dust mulching and by permitting the land to lie fallow to build up moisture for the following crop year. However, the farmers did not know how to conserve their soil and prevent the erosion of semi-arid earth which had been anchored only by the cover-crop of thin grass.

       The great drought of 1932-7 led to the Dust Bowl and caused the abandonment of vast areas of land. Many people left their farms for California, where they joined other migratory workers in search of jobs as fruit and vegetable pickers.

      Meanwhile the American government, with Franklin D. Roosevelt as president, took action to aid the ravaged area. Starving cattle were moved to better ranges, or bought and slaughtered. Loans were extended to the distressed farmers. Mortgage foreclosures were stopped in 1933 by the extension of government credit. Soil erosion was attacked by encouraging farmers to use more effective methods of keeping their land in condition, and a great irrigation program was begun.

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      The great rift valleys of the earth took shape during the Pleistocene age, about two million years ago. They were caused mainly by volcanic eruptions powerful enough to split a mountain range, thus creating a rift between the two sides of the volcano.

       Rift valleys are to be found in all parts of the world where volcanic action has been common. The most impressive example is the Great Rift Valley which extends from Jordan in south-west Asia to Mozambique in southern Africa. Many big lakes are situated within the valley’s boundaries.

       Extremely steep edges are characteristics of these valleys. In Africa their edges rise to heights of 10,000 feet on either side.

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