LITERARY NOTICES. 



H7 



But our dull imaginations have too much in 

 common with the sluggish physical movements 

 of our islaud-home for us to soar to the heights 

 of calculation which seem so easy to Mr. Southall. 

 " It is in dealing with the age of the great ex- 

 tinct mammals that our author shows most con- 

 spicuously this tendency to shirk (unconscious- 

 ly, of course) the difficulties with which the 

 problem is surrounded in Europe. That early 

 man was contemporary in what is now Eng- 

 land, Southern France, and Germany with the 

 lion, the bear, the hyena, the gigantic elk, the 

 reindeer, and the mammoth, the conditions un- 

 der which their bones are found intermingled 

 have long placed beyond reasonable doubt. In 

 the case of the reindeer and the mammoth, the 

 evidence is raised to certainty by the discovery 

 of outlines of those animals etched, with rude 

 but highly-expressive art, upon fragments of 

 bone." 



Chemical and Geological Essays. By 

 Thomas Sterry Hunt, LL. D. Second 

 edition. Salem: S. E. Cassino. Pp. 

 536. Price, $2.50. 



We noticed this admirable volume upon 

 its first appearance three or four years ago, 

 and are glad to observe that it has passed 

 to a second edition. The plan of the work 

 is not changed, as its essays have some- 

 thing of an historical import, which it was 

 thought inexpedient to disturb, so that in 

 the work of revision the author has confined 

 himself to the correction of typographical 

 errors in the text. But he has prefixed to 

 the volume an elaborate essay of very great 

 interest upon questions connected with the 

 general scope of the work, upon which de- 

 cided progress has been made since the 

 first publication, and these additions are 

 well worth the price of the new edition. 

 We quote a portion of this preliminary es- 

 say, which treats of the ancient constitu- 

 tion of the air, and from which the author 

 rises to the consideration of cosmical at- 

 mospheres and the diffused medium of ce- 

 lestial space: 



" On pages 46-48 is a suggestion, made many 

 years since, regarding the question of the tem- 

 perature of the earth's surface in former geo- 

 logical periods, which, from its bearings, both 

 direct and indirect, on some recent geological 

 theories, calls for further notice. From the 

 great amount of carbon and hydrocarbons of 

 organic origin found in the rocky strata of the 

 earth, it has long been inferred that the atmos- 

 phere of earlier times must have contained a 

 large quantity of carbonic dioxide (carbonic 

 acid) which yielded up its carbon for the nutri- 

 tion of the ancient floras. From this the late 

 Major Edwin B. Hunt concluded that, the atmos- 



phere in former periods being much denser than 

 at present, the temperature at the earth's sur- 

 face, due to solar radiation, would be greater 

 than now. It was subsequently pointed out by 

 the present writer that, as already shown by 

 Tyndall, the relations of carbonic acid to radiant 

 heat are such that a quantity of this gas too 

 small to affect considerably the weight of the 

 atmospheric column would, by preventing the 

 loss of heat, suffice to produce a tropical tem- 

 perature over the earth at the sea-level. 



" The quantity of carbon which has been re- 

 moved from the air by vegetation in past ages 

 is, however, very considerable. In a communi- 

 cation by the writer to the American Associa- 

 tion for the Advancement of Science, at Buffalo, 

 in 1866, it was stated that the whole amount of 

 free oxygen in the present atmosphere is no 

 more than sufficient to form carbonic acid with 

 the carbon of a layer of coal covering the globe 

 one metre in thickness, and that the aggregate 

 of carbonaceous matter in the earth's crust 

 would probably much exceed this. Such a layer 

 of coal, of specific gravity 1.25, would have a 

 weight equal to 3,160,000 gross tons to the 

 square mile; while Mr. J. L. Mott, in a commu- 

 nication to the British Association for the Ad- 

 vancement of Science, in 1877, estimates the 

 total amount of carbonaceous substances in the 

 earth at not less than 3,000,000 tons of carbon 

 to the square mile, and probably many times 

 greater. This minimum amount of pure car- 

 bon is equal to 600 times the present amount of 

 carbonic acid in the atmosphere, or to nearly 

 one-fourth its entire volume ; and, inasmuch 

 as the fixation of carbon by vegetation liber- 

 ates a corresponding volume of oxygen, would 

 represent, according to him, a greater amount 

 of this gas than the present atmosphere con- 

 tains. In addition to this, it must be considered 

 that the composition of the various hydrocarbon- 

 aceous minerals shows a deoxidation not only 

 of carbonic acid but of water. The amount of 

 liberated oxygen derived from water equals, for 

 the various coals and asphalts, from one-eighth 

 to one-fourth, and for the petroleums one-half 

 of that set free in the deoxidation of the car- 

 bon which these hydrocarbonaceous bodies con- 

 tain. To this must be added also the oxygen 

 set free in the generation of metallic sulphides 

 by the deoxidation of sulphates, which is ef- 

 fected through the agency of organic matterB, 

 aDd indirectly liberates oxygen. Acainst this 

 we must, however, set the unknown but very 

 considerable amount of oxygen absorbed in the 

 peroxidation of ferrous oxide liberated in the 

 decay of the silicates of crystalline rocks; which 

 may, perhaps, serve to explain the disappear- 

 ance from the air of the whole of this excess of 

 oxygen. 



" The terrestrial vegetation and the air- 

 breathing fauna, which we find from Palaeozoic 

 ages, are, it is unnecessary to remark, incom- 

 patible with an atmosphere holding one-fourth 

 its volume of carbonic acid, and the difficulty of 

 the problem is greatly increased when we con- 

 sider that this amount, corresponding to the 

 carbon fixed in the earth's crust in deoxidized 



