34 



SCIENCE-GOSSIP. 



AN INGENIOUS GLACIATION THEORY. 

 By G. W. Bulman, M.A., B.Sc. 



/^F the many attempts to account for the Glacial 

 ^-'^ period which have been put forward at various 

 times, none have hitherto been able to stand the 

 strain of adverse criticism. Yet of glacial theories, 

 as of Virgil's golden bough, it may be said, " Primo 

 avulso, non deficit alter," and the hypothesis set 

 forth by Mr. Marsden Manson, C.E., in a paper 

 read before the Technical Society of the Pacific 

 Coast (1), seems worthy of attentive consideration. 

 In brief outline the hypothesis is as follows. 



At some point of its past history as a cooling 

 body, the earth must have possessed a surface 

 heat of 212° F., or upwards. Water could not at 

 that temperature remain as liquid on the surface, 

 but would form a dense cloud above it. In the 

 upper parts this vapour would condense, and fall 

 as rain ; but so long as the temperature remained 

 near 212-, it would be immediately driven off again 

 as vapour. Thus the greater part of the terrestrial 

 water substance would exist as a vapour screen ; 

 and this screen, so immensely greater than our 

 present cloud envelope, it is supposed, would 

 effectually prevent the loss of earth heat, and 

 exclude solar rays. Consequently the climates of 

 the earth, instead of being under the control of 

 solar heat as at present, would depend on earth 

 heat alone. As a consequence of this, a uniform 

 climate would prevail from the poles to the 

 equator. In this way the theory accounts satis- 

 factorily for the geological fact of the remarkable 

 uniformity of climate in past ages. 



Mr. Manson enunciates his theory as follows, in 

 the form of a proposition, which he afterwards 

 proceeds to prove : " Given a heated globe, consti- 

 tuted and circumstanced as the earth, and whose 

 surface temperatures, by reason of internal heat, 

 are above the boiling-point of water, to prove that 

 before its surface temperature can pass under the 

 control of solar heat the continental areas must be 

 glaciated." 



The climate of a globe thus circumstanced would 

 be entirely independent of solar heat, for the thick 

 screen of vapour would effectually prevent the 

 solar rays from reaching it. At the same time, 

 its own heat would pass through such a screen so 

 slowly, that its temperature would be retained at 

 212°, or upwards, for long ages. Further, the 

 sun's rays, by heating the upper layer of this 

 vapour screen, would likewise tend to retard the 

 cooling of the earth. According to Mr. Manson's 

 theory, this temperature must have been retained 

 through the geological epochs up to post-tertiary 

 times. The earth radiating its internal heat 

 Q) "Transactions," vol. viii. No. 2., 1891. 



equally in all directions, the region of the poles 

 would be as warm as the equator. This is a 

 strong point in the theory, for it thus accounts in 

 a satisfactory way for the remarkable fact, above 

 referred to, of the uniformity of climate in the 

 past, as indicated by geology. 



It is, however, this very point in the theory 

 which brings it into violent contact with the recent 

 researches of eminent physicists, concerning the 

 secular cooling of the earth. At no period later 

 than 10,000 years from the first solidification of 

 the earth, says Lord Kelvin, could its own internal 

 heat have appreciably affected its climate. If this 

 is so, then obviously the climate of the earth 

 cannot have been under the control of its own heat 

 from Cambrian to the close of Tertiary times, as 

 Mr. ^lanson supposes. In this connection, how- 

 ever, it may be asked, has Lord Kelvin sufficiently 

 taken into account the retardation to the cooling 

 of the earth which a thick vapour screen would 

 effect ? 



Granted, then, such a vapour screen, let us 

 consider what would happen as the temperature 

 gradually sank, and solar heat was finally able to 

 reach the earth. In its uppermost layers the cold 

 of space would cause the formation of snow and 

 ice, but as this fell it would pass through the 

 w^armer layers, and be melted long ere it reached 

 the earth. By slow and almost imperceptible 

 degrees, during the long geological ages, the snow- 

 line would descend nearer and nearer the earth. 

 At length it would reach it, and snow would begin 

 to accumulate. This would be the inauguration of 

 the Glacial period, and the climate of the whole 

 globe would become arctic. The continued snow- 

 fall and the very small quantity returned from 

 the earth as vapour would gradually clear the 

 atmosphere, and in time the influence of. solar 

 heat would make itself felt on the earth. First 

 round the equator the snow would be melted and 

 the climate ameliorated. Water would remain 

 permanently on the earth, and its climate would 

 gradually pass more and more under the control of 

 solar heat as the cloud screen disappeared. 



Obviously, according to this theory, there has been 

 only one great Glacial period, and hence all evidence 

 of glaciation in Tertiary and Pre-tertiary times is 

 against it. Such evidence has been diligently sought 

 for by advocates of many Glacial epochs, and they 

 claim to have found it. On the whole, however, it 

 cannot be said that such evidence as has been 

 brought forward is as satisfactory as might be 

 desired, or that the question has been decisively 

 settled in favour of many Glacial epochs. Perhaps 



