2 3 4 THE POPULAR SCIENCE MONTHLY. 



operative had been at work in remoter times. The existence of a sub- 

 tropical Miocene flora near, and probably up to, the North Pole, with 

 remains of the mastodon, elephant, rhinoceros, and cognate mammals 

 as far north as the icy circle, might be taken to point to a revolution of 

 a terrestrial, if not of a cosmical, kind from higher conditions of tempera- 

 ture. On the other hand, the dispersion in a southern direction of er- 

 ratic blocks, evidently carried by ice-action, and striated or polished by 

 glacial friction, was a proof of a cold climate extending much farther 

 south than that of the present time, invading. even the subtropical lati- 

 tudes. Now, there can be absolutely no room for the hypothesis of any 

 appreciable change, within Miocene times at least, in the total tempera- 

 ture of the earth, either from the sudden outburst of subterranean fires 

 on the one hand, or from general cooling of the earth's mass on the other. 

 At the same time, a large body of both organic and inorganic evidence 

 supports the view that the climate of earlier geological periods, from 

 whatever cause, had over wide regions been in excess of what it now 

 is. Not only in the greater part of the Miocene and Eocene epoch? 

 did a vegetation like that of Central Europe in our day extend into the 

 Arctic regions as far as they have been explored, and probably to the 

 Pole itself, but in the Secondary or Mesozoic ages the prevalent types 

 of vertebrate life indicate a warm climate and an absence of frost be- 

 tween latitude 40 north and the Pole, a large ichthyosaurus having 

 been found in latitude 77 10' north. Carrying our retrospect back to 

 the Primary or Palaeozoic ages, we find an assemblage of plants which 

 implies that a warm, humid, and equable climate extended from the 

 30th parallel of north latitude to within a few degrees of the Pole, 

 while a still older flora, the Devonian, leads to a similar inference. 

 Such, moreover, is the general resemblance between the whole inverte- 

 brate fauna of the Devonian, Silurian, and Cambrian rocks and that of 

 the Carboniferous, Permian, and Triassic series, as to make it clear 

 that a similarity of conditions as regards temperature prevailed 

 throughout the whole of these six periods. 



The idea of possible variations in the temperature of space trav- 

 ersed by our globe, started by Poisson, is promptly set aside by con- 

 siderations long ago advanced by Mr. Hopkins. Nor is there much 

 greater force, as Sir Charles Lyell amply shows, in the effect attributed 

 by others to variation in the obliquity of the ecliptic. The latest cal- 

 culations of Sir John Herschel conveyed in a letter to our author, in 

 October, 1866, admit the possibility of a deviation of the earth's axis to 

 the extent of three, or even four, degrees on either side of the mean. 

 The sun's rays would thus be disseminated at intervals over a far 

 broader zone than at present, around the Arctic and Antarctic Poles, 

 with a corresponding shortening of the Polar night, and a diffusion of 

 more genial warmth. Yet, on the other hand, a large deduction must 

 be made, as Mr. Meech has shown, for the increased length of path, 

 and the greater amount of atmosphere through which the calorific raya 



