IN TOUCH WITH NATURE

Otago Daily Times, Issue 22068, 26 September 1933, Page 2

IN TOUCH WITH NATURE

SILURIAN DAYS. MILLIONS OF YEARS AGO. By J. Drummond, F.L.S.. F.Z.S. Inhabiting the borderlands of Wales, the Silures, about a.d. 50, resisted the Roman legions stubbornly. The Roman general, exasperated by their obstinacy, declared that not only they but even their name would be blotted oiit. Some 1800 years later Sir Roderick Murchison, geologist, discovered in the country where the Romans and the Celtic race had fought a series of rocks characterised by sandstones, shales, and limestones. Intermingling history, romance,_ sentiment, and geology, he named the series Silurian, restoring the Silures to renown and perpetuating their bravery in imperishable stone. He linked them with one of the most important periods in the world's history and one of the most interesting. It began when Silurian rocks were first laid down, about 400,000,000 years ago if the geological dock is read • accurately by the flickering light of radio-active substances. It continued for about 40,000,000 years. It slipped imperceptibly into the Devonian Perod, some of whose obscure history was elegantly written by Hugh Miller under the more picturesque title Old Red Sandstone.

Silurian rocks, holding dim records of Silurian life, rest in many parts of the world. They occur in the Appalachian Mountains of "New York State, in niany other North American districts, in England, Scotland, and Ireland, in Western China, Northern India, Scandinavia, Rua; sia, Brazil, Burma, Peru, Bolivia, Australia, and New Zealand. The presence of great numbers of corals show • that Silurian seas were warm, in keeping with a mild climate almost all the world over. Large deposits of rocksalt in North America are evidence that the climate there was even arid. Excessive evaporation' of eea water in shallow depressions caused salt to precipitate. Those rocksalt beds, are from 40ft to 80ft thick. They cover an area of about 10,000 square miles. The seas, mostly, were shallow and clear. They were thick with moluscs, crustaceans, and fishes. Lamp-shells, trilobites, ammonites, plant-animals that lived in seaweeds, delicate sea lilies, sea urchins, eea scorpions, sand fleas, star fishes, king crabs, and sea squirts jostled one another.

The earliest records of ancestors of the pearl oyster and of the mussel are in Silurian rocks. The fishes were well armed, some with plate armour in the form of bony plates. - Many resembled sharks of our own time. Little is known of vegetation or animal life on Silurian continents. There were liver-worts, ferns, and mosses. The earliest scorpions date back to Silurian times. Insects, doubtless, were plentiful. Trilobites, remarkable crustaceans, had had their day and had started on the path to extinction; but there arose in Silurian days an extraordinary race of gigantic crustaceans. Some species of these were from a foot to a foot and a-half long. Others were six feet, which shows that the conditions were congenial and that food was ample. Although amphibians, reptiles, birds, and mammals were absent, forms of invertebrate life were not primitive. Their complexity discloses ancient lineages in even that early stage of the world s childhood.

The manifold Silurian sea-life contributed to the present world's useful possessions limestones that yield lime and building-stone. Rock-salt from the shallow lagoons and the "land-looked seas is very valuable. Professor J. Park, of Dunedin, found that many Silurian trilobites and lamp-shells in New Zealand are almost identical with species characteristic of Silurian life in England and in North America, but that New Zealand's Silurian life is unlike Australia's. He accepts this as indicating that in the Silurian Period there was a continuous sea-lit-toral between New Zealand, America, and North-west Europe, and that .between New Zealand and Australia there was a deep sea that those creatures would not enter, or a land barrier. Silurian rocks s>t Ludlow, England, contain the Bone-bed; This'is a thin bed filled with the bones and spines of Silurian fishes and with fragments of the six-foot crustacean.

Except for the advances of seas on the continents and the withdrawal of the waters again, ihe face of the :earth was tranquil for most of this long and momentous period. ' Before it ended forces stored for millenniums in the interior of the earth thrust, folded, compressed, and crumpled the rocks; Volcanoes burst out. Mountains were built up. One mountain range, extending from Spitzbergen through Scotland, England, Ireland, and France, is believed to have been larger and loftier than the present Swiss Alps. At the close of the following period the range had been reduced to a series of rolling plains, and water lapped or covered proud summits.

The Old Red Sandstone was formed from the ruins of land that had been uplifted in the Silurian Period. The relationship between land and water in the Silurian Period exemplifies the changes that even continents undergo in a changing world. Landscapes alternated with seascapes, hills and valleys with plains. "Ocean tides Have ebbed and flowed where the Rocky Mountains push their summits 14,000 feet above sea level," an American geologist wrote. "Marine fossils are found in rocks 10,000 feet above sea level. j What assurance have we that the Rockies will not again bathe their feet in.the waters of the Atlantic, and that the Great Plains will not again be an'ocean's bed? " « ■ ■

Mrs J. Bryson, of Carlon avenue, Wanganui, reared four kingfishers in her aviary. After they had been in a large cage for about a year, she discovered that they_ had killed and eaten some of her captive white-eyes and zebra finches, and had injured her canaries. She placed the kingfishers in a smaller cage of their own. She writes:.—"l have a tank of water in that cage. Every morning, as soon as the sun is up, the kingfishers dive into the water at great speed. It is interesting to watch them setting worms and small fishes out of the water. Thev are as quick as lightning. Usually they are very quiet birds, sitting on branches for hours. They seem to come to life suddenly, and make up for lost time. When I am in luck with my mouse-traps, my kingfishers have a gorge. They devour mice of fair size without anv trouble. Having done so. they sit with their chests sticking out. full of mouse, the tails hanging out of their bills. I have had whiteeyes in the aviary for the past four years. They sine very sweetly, and in the winter they look in better condition than the wild ones."

Mr H Fildes, Wellington, agrees that the Australian magpie is one of the most popular birds introduced into New Zealand. He writes: "It is blamed for attacking, killing, and eating oth Pr birds. Its detractors are not very familiar with its habits and proclivities, necqssnrv to its existence. Dr G. Bennett, in "Gatherings of a Naturalist in Australasia." 1860 wrote: The magpie is an omnivorous feeder, potatoes, fruit, and bread being eaten, but meat is indispensable to its existence, and it often exercises its shrike-like habit of killing and devouring small birds. I. have known several instances of 'persons, ignorant of its carnivorous propensity, leave canaries in cages on the ground where magpies range. They find the canaries struck on the head and killed by magpies. A dead canary was given to a magpie, which tore it to pieces and devoured it.'"

To encourage magpies in gardens and near dwellings, Mr. Fildes suggests that people should supply them with meat food, particularly in the nesting season. It is not out of place to refer again to the opinion of Mr W. R. B. Oliver, director of the Dominion Museum, Wellington, a man of sound judgment. Magpies, perhaps more from curiosity than anything else, he writes, occasionally pull up seedlings, and sometimes kill small birds, but, to farmers, are amongst the most useful birds in the Dominion. Mr Fildes askfl if piping crow is the magpie's other name. It is, and crow-shrike is still another, but this black and white bird with a voice like a flute is usually called the Australian magpie.