NATURALISTS' FIELD CLUB

Evening Star, Issue 20591, 17 September 1930, Page 2

NATURALISTS' FIELD CLUB

SATURDAY’S OUTING The outing on Saturday was to Fraser’s Gully, Kaikorai, where certain matters of geological _ interest were pointed out and explained by Mr H. S. Tily, B.Ss. Their understanding required a knowledge of the geological history of the Dunedin area, and it was explained how at one time the area around Dunedin was depressed bo neath the sea, and then elevated again, and during this time the sedimentary rocks of which the Caversham sandstone is the topmost stratum, were deposited. Then warping took place, and folds were formed which were later to develop into hills much as we have them to-day; also volcanic activity broke out, and the land tilted toward the east. But th e folding was accompanied by much' faulting, and the system of hills and valleys was accentuated by this process. The volcanic action was not continuous, but was intermittent and between successive periods there wore some long intervals of thousands of years in which the country became forested, and small areas of deposition of mud were formed. At ; Fraser’s Gully most of the points are demonstrable. The party left the Rattray street tram terminus, and proceeded up Fraser’s road. At a point on the right just after meeting the hill evidence of folding and faulting is to bo seen in the orientation of pebbles in the bank j it is well known that extensive faulting occurs on the western side of the Waitati, Leith, and Kaikorai Valleys. Further up the valley occur the well-known leaf beds. At one point in the creek bed and another on the slope of the hill the party searched the shaly deposits there found for leaf impressions m the mudstone. Many well-preserved specimens were found. Still further up the valley the walls of the valley were found to be of sand, indicating that the sedimentary rocks which dip eastwards underneath Dunedin, had now risen to the surface, only, however, to disappear again under Mount FlagstaS. INDOOR MEETING.

The indoor meeting on Monday evening was very well attended, when the geological studios of Saturday’s outing wore followed up by a very interesting lecture by Mr Tily on ‘ Earthquakes.’ The subject was dealt with from the point of view of the older earthquake studies, as the new seismology, like most scientific work nowadays, has become exceedingly specialised and re quires the training of an advanced mathematician and physicist for its pursuit. It was stated that the earth s surface is never constant, but is always changing and on the move, by erosion and crustal movement. The earth’s crust, under influences of which as yet we have little knowledge, but probably arising in the earth’s core, is warping and twisting and rising and falling, and it is inevitable under these circumstances that it must often bend so far that it cracks; when it cracks a wave of concussion travels out from the crack, arid it is this concussion that constitutes an earthquake. Apart from earthquakes, fractures of the earth’s crust are well known in geology -is faults, and so it is that earthquakes and faults are-inseparably connected. When an earthquake takes place we look for the fault, and when we find a fault that seems to show recent move ment along its face we say there is the origin of the earthquake. Conversely, areas of recent faulting are areas m which earthquakes may ho expected. Earthquake areas were not,.distributed equally over the whole’ of the earth’s surface, but were collected into zones as if along these zones there were weaknesses in the earth’s crust which yielded to the stress within; it is significant that the volcanic regions correspond with the earthquake regions, indicating that volcanoes and earthquakes probably both have the same cause, and are two different methods of relieving the internal stresses. These zones may roughly be grouped into a band running round the whole'of the Pacific Ocean, and another running from side to side of it through the Mexican Gulf, the Mediterranean, the Himalayas, arid Southern China to Japan. The characteristic features of earthquakes with, _ viz., the peculiar noises before, during, and after, the shocks, the liefore and after shocks, their occurrence in lines, the mud and water geysers, and alterations to drainage. Particular reference was made to Up recent earthquake in the north-west portion of the South Island. The full report of this disturbance has not yet been published, but from the accounts to hand it appears that a block of lan I about twenty miles wide and of unknown length rotated about a north east and south-west axis (the general direction of New Zealand). The rota tion was such that the eastern side sunk at White’s Creek fault, and the western side rose at the Korigahu fault; The places that suffered most wore Ka ramea and Westport, both of which lie along the direction of the _ Kongnhu fault, and Murchison, which is close to the White’s Creek fault. Amongst the typical earthquake phenomena on this occasion were the before and after shocks and noises, the rising and fault ing of the land along the fault lines, the destructive waves at Lake Rotoroa. the flowing backwards of the Gowans River, the huge landslides and geysers oi water and mud, the disappearance of a stream at Karamea. Photographs and slides of many of the scones in the disturbed area were shown together with pictures of typical scones in other parts of the world. A very hearty vote of thanks was ac corded Mr Tily for his interesting lec turn.

Among other exhibits of interest a photo of the skull of a notornis found at Waitati in 1896, was shown on the screen by Mr L. M. M'Caskill.