NATURALISTS’ FIELD CLUB

Evening Star, Issue 20254, 15 August 1929, Page 14

NATURALISTS’ FIELD CLUB

VISIT TO NICOL’S CREEK On Saturday afternoon members of tlio Field Club paid a visit to Nicol’s Creek, the object of the cxciirsioii'being to' observe the very acute fold. in the rock strata which is evident in that area. As tho bed of the creek was traversed from the Leith Valley road upwards, it was noted, that the strata exposed on the walls of the creek were approximately horizontal; then, at ,a point just a little below the first waterfall, they took a bend upwards, and at the fall itself were standing almost vertical. Weather conditions and time did not permit of further explorations up the bed of this creek, but if a further traverse had been made it would have been found that the tilted strata continued for some distance and.then changed from volcanic rocks to sedimentary rocks, showing that the sandstones, marls, and other rocks whicharo found at Green Island underly the volcanic rocks of Dunedin, and had shared in the land movement which bent and tilted the volcanic rocks. The tilted strata finally end in a fault, which in Nicol’s Creek is coincident with a phonolitic dyke, and the rocks from that point to the top.of the mountain are volcanic strata, again approximately horizontal, so that during the complete traverse of Nmol’s Creek the same rocks can be met with three times; first, as they lie horizontally in the order; second, as they lie tilted in the order; and, finally, in the same order as at first INDOOR MEETING. At the indoor meeting, held on Monday evening, Mr W. J. Williams gave a vci'y interesting ml dress on ‘ Elementary Meteorology.’ In opening his address Mr Williams quoted these words from ‘ Everyone’s Book of the Weather,’ by A. T. Williams; “In these days of wireless reports, meteorological charts, and forecasts, journeys by aeroplane or airships, scientific farming and plantation work and the like, interest m the weather is becoming more and more widespread, and a knowledge of atmospheric phenomena is useful as well as fascinating.” Continuing, Mr Williams stated that the actual height of the atmosphere above tho earth is unknown, hut it was generally. believed to be limited to 150 or 200 miles. Regarding the temperature of the atmosphere, although the earth was entirely dependent on the sun for heat, the proximity of the earth to the >-un did not determine the amount of heat received on tho earth. This was regulated by the angle at which the sun’s rays readied tlio earth. Evaporation was the process by which a liquid or a solid became changed into a gas, but so far as the atnioaphere was concerned it was. sufficient to- consider only the conversion of water into vapour. Tho rate of evaporation depended on several factors, which included tho -temperature, exposure of the surface and the state of saturation, and pressure of tho enveloping air. If water was spilled on an impenetrable surface it dried up, or, in other words, was converted into invisible vapour, at a rate which depended on tho temperature, being quicker on a warm day than on a, cold one, and also quicker on a windy day than a calm. day. All evaporation was accompanied by a. loss. of temperature of tho surface from which evaporation took place. Vapour was really the term applied to. designate the gaseous form which a liquid or solid substance assumed when heated. Water vapour evaporated from the surface of the land, and water was always present mixed with tho air.

Water vapour of tho atmosphere was practically the same as sterna, and its action in' the atmosphere was similar to that of a'sheet of glass which _ admitted the sun’s rays and then retained the heat. The amount of water vapour field in tho, atmosphere at any time was termed the degree of humidity. Condensation of vapour was caused by cooling. Thou the ■ molecules of condensed water vapour drew together and formed drops of liquid. Water was evaporated from the earth, and, as the vapour was lighter than air, it rose rip until it reached a height whore the temperature was lower, when it condensed and formed clouds. Tho minute globules of water composing the cloud wore believed to bo in a, continual state of motion, tending to sink downwards by the action of gravity until they poached tho lower layers of the clouds whore the temperature was higher, thou wore again evaporated, changing once more into vapour. Tho heat received by tho earth was stored by it to a few inches in depth at its surface, but the heat which fell _nn the sea was diffused through a considerable depth. The actual surface of the earth was therefore at a higher temperature than the surface of the sea. The. formation of clouds and their significance in tho matter of weather forecast was also dealt with/ and Mr Williams illustrated his lecture throughout with pictures, charts, and gliagrams. At tho conclusion of his address he was accorded a hearty vote of thanks.