Wellinr/ton PhilosupJnail Society. 59l 



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 jDroduces 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 Aixhipelago and South Europe, and we find a 

 thickness of stratified dejDosits about 400 times the thickness of the same 

 formations to the right or left. This is a common feature of all great moun- 

 tain 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 i-emoved 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 3'et 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 wdth 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. Eegarding 

 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 pre- 

 sence of the atmosphere. Eemove 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 Coccida, 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. 



