■544 report — 1878. 



5. The Geological Relations of the Atmosphere. 

 By T. Steret Hunt, LL.D., F.R.S. 



The author began by noticing the inquiries of Ebelmen into the decomposition 

 of rocks through the influence of the atmosphere, resulting in the fixation of car- 

 bonic acid and oxygen, and discussed the question at length, with arithmetical 

 data. He inquired farther into the fixing of carbon from the air by vegetation 

 with liberation at the same time of oxygen both from carbonic acid and from the • 

 decomposed water, the hydrogen of which with carbon forms the bituminous coals 

 and petroleums. It was shown that the carbonic acid absorbed in the process of 

 rock-decay, during the long geologic ages, and now represented in the form of car- 

 bonates in the earth's crust, must have equalled probably two hundred times the 

 entire volume of the present atmosphere of our earth. This amount could not, of 

 course, exist at any one time in the air : it would at ordinary temperature be lique- 

 fied at the earth's surface. When came this vast quantity of carbonic acid which 

 must have been supplied through the ages ? The hypothesis of M. De Beaumont, 

 who supposed a reservoir of carbonic acid stored up in the liquid interior of the 

 planet, was discussed and dismissed. The gas now evolved from the earth's crust 

 from volcanic and other vents was probably of secondary origin and due to carbo- 

 nates previously formed at the surface. 



The solution of the problem offered by the author is based upon the conception 

 that our atmosphere is not terrestrial, but cosmical, being a universal medium 

 diffused throughout all space, but condensed around the various centres of attrac- 

 tion in amounts proportioned to their mass and temperature, the waters of the 

 ocean themselves belonging to this universal atmosphere. Such being the case, airy 

 change in the atmospheric envelope of any globe, whether by the absorption of the 

 disengagement of any gas or vapour would, by the laws of diffusion and static 

 equilibrium, be felt everywhere throughout the universe, and the fixation of car- 

 bonic acid at the surface of our planet would not only bring in a supply of this gas 

 from the worlds beyond, but, by reducing the total amount of it in the universal 

 atmosphere, diminish the barometric pressure at the surface of our own and of 

 all other worlds. 



This conception of a cosmical atmosphere of which our own forms a part is not 

 new, but was put forth by Sir William R. Grove in 1843, and is developed in the 

 very learned and ingenious work of Mr. Mattieu Williams, on ' The Fuel of the 

 Sun,' and has lately been noticed by Dr. P. M. Duncan in its geological bearings. 

 Ebelmen, in 1845, pointed out that the greater weight of an atmosphere charged with 

 carbonic acid would increase the temperature due to solar radiation at the earth's 

 surface, and greatly modify atmospheric phenomena. Tyndall, by his subsequent re- 

 searches on radiation, showed that certain gases, in amount too small to affect con- 

 siderably the barometric pressure, might influence powerfully climatic conditions, 

 and suggested that in the former presence, in the atmosphere, of moderate quantities 

 of a gas like carbonic acid might* be found a solution of the problem of the cli- 

 mates of former geologic ages. According to the author, the amount of this gas, 

 which, since the advent of life on our earth, has been subtracted from the univer- 

 sal atmosphere," although it may not have sufficed to diminish by more than a 

 small fraction the pressure at the earth's surface, would account for all the con- 

 ditions of geological history so far as temperature and climate are concerned. 



He maintains that while we have evidence of a warm or sub-tropical climate 

 prevailing over the Arctic regions from the Carboniferous down to the Lower Creta- 

 ceous times, and a gradual refrigeration up to the temperate climate of the Miocene 

 age, we had for the first time in the Pliocene age the evidence of Arctic cold, which, 

 with some variations, has continued until now. Since that date geographical varia- 

 tions have caused and may again cause local climatic changes of considerable mag- 

 nitude ; but no such changes could permit the existence, over continental areas 

 within the Arctic circle, of such tropical vegetation as we know to have once 

 flourished there. Geographical changes, as Dr. F. Campbell Dawson and others 

 have so well pointed out, might lift large areas into the region of perpetual frost, 

 and thus give rise to local glacial phenomena, and may, moreover, account for con- 



