Third Meeting: 25th August, 1886.
Dr. Hector in the chair.
New member.—H. A. Gordon, F.G.S.
Papers.—1. “Notes in Reference to the Prime Causes of the Phenomena of Earthquakes and Volcanoes,” by W. T. L. Travers, F.L.S. (Transactions p. 331.)
Mr. Crawford doubted if volcanoes were chiefly situated in tropical regions. He had been surprised to hear of late that the supposed craters in the moon were really made of ice. This would need explanation.
Mr. Hudson made some remarks regarding the fluid condition of the earth's interior not being compatible with the observed effects of the moon's attraction.
Mr. George referred to the difference in temperature of interior of the earth in different countries.
Mr. Maxwell said the contraction of the earth's surface was a prime cause. The earth's interstitial friction was sufficient to generate heat, which, when water is brought into contact with the heated parts, quite explains the explosions that take place.
Dr. Hector considered that the causes referred to by the author were very remote from the causes of the earthquakes and volcanoes of the present, or, indeed, any past geological period which we can study. How the globe solidified and assumed its present form is not the question: but what is the nature and origin of the force that produces the great mountain chains and the ocean beds? If we could drain the ocean-beds, we should find them only bordered by volcanic rocks, that occupy a very insignificant proportion in the Earth's crust, as compared with the stratified rocks. Take a line, for instance, from New Zealand in a great circle to the north-west, through the Indian Archipelago and South Europe, and we find a thickness of stratified deposits about 400 times the thickness of the same formations to the right or left. This is a common feature of all great mountain regions; in fact, there had been a steady depression or inflexing of the Earth's surface, in which deposits of sediment are continuous, until more than 30 miles' thickness had accumulated in that particular line. Then followed a great elevation, or reversal, of the same flexure, so that the sediments are largely removed by denudation, and the basement formation or rocky core of the original surface crust is actually laid open to view. Here, therefore, we have evidence of the Earth's surface having been engulphed to at least 30 miles; and yet in such mountains as the Himalayas, or Alps, volcanic rocks are almost wanting, the igneous rocks present being mainly such as result from deep-seated crushings. If we were dealing with a globe having only a thin shell, resting on a fluid, such flexures would necessarily have been accompanied by most terrific protrusions of the interior matter. Regarding the temperature of the Earth, it has been found that in the Sierra Nevada, in the Comstock lode, when they had gone down 2,000 feet, a temperature was reached at which the men could not work; water gushed from the rock at 145° Fahr., and the temperature could not be kept below 100°. That was 4,000ft. above sea-level, the mouth of the mine being at 6,000ft. At Stawell, in Victoria, the mines start at 800ft. above sea-level, and go down 2,400ft., that is 1,600ft. below sea-level; yet the miners are not in the least degree inconvenienced by increased heat. That shows that the increase of temperature must have been caused by other circumstances than the central heat of the earth. With regard to the objection offered by Mr. Crawford as to the ice on the moon, he mentioned a most interesting paper in “Nature,” taken from an American source, by John Ericsson, who shows that a body exposed to space without an atmosphere would be reduced 142° below zero when turned away from the sun; while the side turned towards the sun would never be above 81° below zero.
Mr. Travers, in reply to Mr. Crawford, stated that we know perfectly well that the existence of water on the globe depends entirely on the presence of the atmosphere. Remove the atmosphere, and all the water would ascend into space and be diffused in the form of aqueous vapour. As to the surface of the moon being encrusted with ice, the theory is certainly new, and at variance with all telescopic observation. He then referred to the strides made in lunar photography, and upheld the other theories he had advanced.
2. “On the Honeydew of the Coccidœ, and their Fungus,” by W. M. Maskell. (Transactions, p. 41.)
Mr. H. Travers said that the black fungus found on leaves was the scaly blight.
Fourth Meeting: 8th September, 1886.
Dr. Hector in the chair.
Papers.—1. “On Polynesian Folk-lore,” by E. Tregear. (Transactions p. 486.)
2. “On a new Species of Moth, (Pasiphila lichenodes), by A. Purdie, M.A. (Transactions, p. 69.)