TRANSACTIONS QF THE SECTIONS. 55 



with brown-coal, and the gi'eat gold-diift, as shown by special maps and sections. 

 East of the schistose country are — (1) inclined sandstones, with estuarine shells, 

 and excellent brown-coal ; (2) marine clays, with septaria ; and (3) the white 

 'crag.' Some marine beds, possibly contemporaneous, also occur near the coast. 

 The carbonaceous beds may possibly be Upper Mesozoic, the others are Tertiary. 

 There are also extensive alluvial deposits. Volcanic rocks occiu- at Otago Harbour, 

 and elsewhere near the eastern coast, and are of late Tertiary age. The author 

 thinks that the coimtry was higher, and glacial action greater, in Post-tertiary times 

 thaq flow, but that no great or general submergence has taken place since. 



On the Possible Conditions of Geological Climate. 

 Bii Professor Hejo^esst, F.R.S., M.B.I.A. 

 It appeared to the author that we have now attained to a sufficiently complete 

 knowledge of the causes which atiect the earth's existing climate to attempt the 

 investigation of the climatic condition of ditferent geological epochs, with a view 

 of arriving at results capable of being verified by the fiicts accumulated by geolo- 

 gical observers. The principal active conditions upon which climate depends are 

 (1) the temperature of^space and the intiuence of stellar irradiation ; (2j the sun's 

 intensity and the earth's position in its orbit; (.3) the amount of heat gained by 

 the superficial parts of the earth from its interior. The secondaiy conditions of 

 climate are the absorbing, radiating, and conducting powers of the matter com- 

 posing the earth's exterior coating, as well as the state of consistence in the solid 

 or fluid form of the several parts of this coating. The author referred to the 

 possible variations of the fii-st primary source of heat as suggested by Poisson — 

 namely, that the temperature of space may be variable, and thus that the earth, 

 moving with the sim and the rest of our sj'stem, might be alternately warmed and 

 cooled by passing, after the lapse of ages, through regions of space with very dif- 

 ferent thermal conditions. He had already criticized this speculation at the 

 Meeting of the Association in Manchester in 1861, when it had been referred to as 

 a possible agent of geological change by Professor W. Thomson. The author 

 pointed out that no evidence could be presented of variations of temperature in 

 space, except those which may result fi-om varying radiation. If the stars are 

 heat-giving as well as luminous, they radiate heat to smTOundiug bodies inversely 

 as the squares of their distances. The correspondence between this law and the law 

 of gravitation would lead to the inference that our sim could not approach so close 

 to another star as to intiuence teiTestrial climate to the large extent required by 

 many geological phenomena without producing a permanent connexion between 

 the two Sims, so that the double system would become, in fact, a double star. 

 This objection coidd not be met, and it has been since reproduced by a recent 

 writer in the pages of one of our scientific periodicals. The researches of chemists 

 and physicists into the physical constitution of the sun present grounds for believ- 

 ing that the sun's intensity may possibly be a variable quantity. The ingenious 

 speculation of Mayer, by which the sun's heat ia attempted to be explamed on 

 thermodynamical pruiciples, deserves notice, because it has been appealed to in 

 order to fui'nish some presumption of past variations in solar intensity. The sun, 

 accQvding to this theory, is fed, and has been nom'ished for ages, by mjTiads of 

 aerolites, such as we know to exist in space. It has been shown that the fall of a 

 single aerolite on the sim would produce by its percussion a calorific effect so 

 enormous that we may readily admit the efficiency of the cause, provided the 

 asteroids are supplied to the sun in large quantities. But how does this theory, if 

 true, tend to explain the past conditions of terrestrial temperature ? The sun, on this 

 hypothesis, draws to it, by the attraction of its overpowering mass, midtitudes of 

 those small planetary bodies which faU in smaller quantities upon the earth. The 

 suu's mass, volume, and surface have, therefore, probably been on the increase 

 since verj' remote epochs. The dynamical heat-producing energy of the sun, as 

 well as its heat-radiating sm-face, would follow a correspondiug law of increase. 

 Thu^ it woidd seem to follow that the sun's intensity should, upon the whole, be 

 greater at recent than at remote geological epochs. The growing mas3 of the sun 

 would also slightly tend to shorten the earth's mean distance, and therefore to add 



