IN TOUCH WITH NATURE.

Otago Daily Times, Issue 20060, 29 March 1927, Page 2

IN TOUCH WITH NATURE.

THE GREAT DULLER FAULT. By J. DRUMMOND, F.L.S., F.Z.S. A sheer wall between the Ngakawau River and the Duller Gorge claims the admiration and the wonder of a Greymouth resident, who, with knapsack on his hack, wandered in that country, watching birds, collecting insects, and gathering 1 wild Howers. The dislocation that built the wall created one of the most remark- ! able scenic features in New Zealand. It is the result of an immense fracture in the rocks, the Lower Duller Fault. Gravel, sand, and mud, deposited ns sediment, is converted into rock. Laid down on the seashore, on the bottoms of lakes, or on river beds, sedimentary rocks originally are horizontal, or slope gently. Stupendous pressure ofte.. folds, crumples, tilts, fissures and fractures them. Like almost every material —iron, lead, and timber, for instance —rocks under sufficient pressure may bend without breaking. They may he folded like cloth, or they may be undulated or minutely corrugated. Several folds may occur in a piece of rock no larger than a man’s hand. A single fold may run through three or four wide districts. Some rocks, responding to the pressure, now stain, up on end. With continued strain, there comes a time when the rocks can bend no more. Break they must. The result is dislocation. This is evidenced in sedimentary rocks almost everywhere by simple joints or cracks. When greater dislocation causes one wall, or both walls, of a fissure to move, a fault is produced. A fault expresses the relief locks seek from pressure when simple joints fail them. Some faults may be traced on the surface for hundreds of miles. In most cases there is no surface feature to proclaim their presence. A line of depression, the displacement of spurs, and other evidence mark the- great Moana-tai-avi Fault, which, traversing the Thames goldfield, displaces all the gold-bearing lodes in its path. The Lower Duller Fault has been mapped for almost 50 miles. It runs along the western base of the Paparoa and Papahua Mountains, and follows the present coastline between Grevmouth and the Karamca Bight. At Kongahu Point the down-throw, or vertical displacement, is between 1000 and 2000 feet. At Granity, it is more than 3000 feet. South of the Duller, it is estimated at 7000 or 8000 feet. Every nook . -d corner of that wonderful district speaks of mime .surable earth movements during the vast ages. Much is sani of the beauties of the Duller Gorge, but how little do we hear of the forces that created them. Many of the prominent land-forms in New Zealand, as in other countries, have arisen from folds and faults, and erosion Rivers and streams act rapidly as denuding agents. Water, (lowing through a rift in compact rock, with a steep grade, makes a narrow rocky channel. When the channel is dorp and has steep sides, as in many New Zealand mountainous districts, a gorge is carved. A gorge sometimes cuts completely and cloanFv through a mountain chain. The Shotover River, Otago, has cut through an old glacial valley, in which, not far from tho river, there is the Shotover Fault. I>ecp .chasms, ravines, and gorges occur in all elevated regions. Canons are defined by Professor J. Park, Dunedin, as profound river-gorges with stoop walls. Early Spaniards in tho Western States of America gave tho name canon to all deep, narrow river-trenches with inaccessible walls. In other countries it is used to mean any nrofonnd defile of groat depth in proportion to its width. The Grand Canon of Colorado is the most remarkable canon system in the world, and tho most stupendous work done by an eroding river. It is a simple but gigantic trench, 218 miles long, from four to 12 miles wide, from 4500 to 6000 feet deep. In parts, the strata are carved into buttes as high as mountains. It was dug out ol tho Colorado Plateau by the Colorado River, which, when arid conditions were established, gave undivided attention to this, the greatest undertaking any river has attempted. Tho Colorado River is old. as the ages of rivers go, but its canon bears tho impress of youth, os geologists regard youth. An Auckland correspondent, who, having watched spiders for many years, has learnt to love them, complains of a statement, on the authority of the “Cambridge Natural History,’’ that all the remarkable and apparently intelligent actions of spiders are . -counted for by obedience to blind ins'.. Tho latest and best observations of spiders are by Dr R. W. G. Kingston, a. member of tho Indian Medical Service. He had unrivalled opportunities for-watch-ing them weaving their geometrical fabrics in tho Himalayas. Ho saw the precision of science blend with the beauty of art. Untiring industry, exact method, faultless accuracy, and inimitable skill raised edifices of mathematical beauty. It might have been tho work of profound wisdom, the product of a calculating mind measuring angles, estimating areas, tracing with skill the geometrical curve, examining tensions, appreciating minute imperfections, halting, reversing, circling backward as perfection required. Still, ilo is convinced that tho spider, living in total ignorance, knows nothing of its wonderful work, whose beauty and precision’ are lost on it. it must work; it knows not why or how. The delicacy of its silken threads, the perfection of it- workmanship, gratify other minds, not tho spider's. “Instinct is tho guiding factor of a spider’s life,” Dr Kingston slates. “Instinct compels it in ono unde via ting course. Introduce difficulties in its circuit, raise increasing barriers to oppose tho instinctive progress, build up obstructions to impede 1 tho blind routine, and the spider can do nothing to overcome them. It can only struggle on its course. It is merely a slave to its own instinct. He who studies for tho first time tho subtle device of a circuJai snaro is full of wonder, is amazed at tht architect’s ingenuity. This is a false impression. There is no skill, no ingenuity in tho sense that man uses it. There is little credit to tho spider, at least to the workings of its mind. It is an automaton. The geometrical spider hoars, tastes and has an exquisite sense of touch, but it lacks tho faintest glimmer of knowledge. Its mind is an utter blank.” If, as Dr Kingston states, spiders are devoid of. Intelligence, instinct is highly developed in (hem. This is demon strated in tho house-spiders, Togenaria, of the family Agelenidce, well represented in New Zealand. If a male house-spider is placed on the web of a female bo vigorously drums on the web. Tho female feels tin web shake and arouses herself, but knows that tho vibrations are not caused by a fly. Waiting expectantly, she allows th • vibrations to play all around her, and the male approaches gradually until ho ran touch her with his forelegs. Mr T. H. Savory, author of a new book on British spiders, in a more recent article in “Discovery,” published in London, slates that a male spider often may be seen lurking on tho outskirts of one of tho beautiful webs of the Epeiridae. Many people believe that he fears for his life. M- Savory questions this belief. “He is 0 i the threads of the web,” Mr Savory slates, “and what airs ho may be playing 01 them we poor humans have no means of knowing. His tune may. probably often docs, surpass the beauty of human choirs to cars capable of appreciating it.” The crab-spiders, which run sideways, an ! which usually lurk in flowers or under fallen leaves and on insects that, approach, have a very peculiar courtship. The female of T'isnura mirabilis demands something | more substantial than dances and antics, j Hoi suitor must wrap up a fly and nre- | sent it, to her. The most, elaborate love | dances are performed by male jumping spiders. They raise their front legs and wave them in tho air, or extend the legs I on ono side and walk in a circle. All the : movements of the dance display most conI spicuously his colours, as if ho knows where i his greatest beauty lies, and wishes to display it. The female, obviouly interested watches intently, turning around in order to keep the male in full view. She sometimes joins in the dance, 'male and female whirling together in ecstasy. The shrill notes of cicadas, probably have ceased in Now Zealand for the season, after crackling in tho forests and on scrublands, and people who give these insects a second thought doubtless no longer wonder what, kind of a musical instrument i (he cicadas use. It is the most perfect ami exquisite device of the kind Dr Kingston has seen. Its parts, examined by hint, correspond to (lie parts of a musical instrument made hy man The supporting structure, a drum, is a. membrane: the vibrating strings are liars; the motive newer is a muscle; and a pointed finger that sounds the long refrain is a tooth. The whelp instrument is described as a wor.deiful example of beauty, sbuplicitv I and strength, without parallel in the insect 1 world.