60 Prohahle Astronomical Causes of 



retain its pristine form long after the spheroidity of that 

 form -was greatly in excess of what it should be from the 

 rate of axial revolution. 



Yenus, on the other hand, ma}^ have retained a large 

 amount of original heat, not because of the vastness of her 

 mass, but on account of radiation being checked by proximity 

 to the Sun. She may, therefore, remain nearly as plastic 

 from this cause as in the far off Jupiter from quite a different 

 one. Hence she is even more spherical than the eart£. If 

 this hypothesis, however, be tiTie, then the earth is even now 

 somewhat more spheroidal than it should be — surmises as 

 to this being the case have, I think, ere this engaged the 

 attention of astronomers. 



Granting that this theory be true, it will readily be seen 

 how the changes spoken of are likely, not only to cause 

 contortion of strata, but also to act upon and alter the mean 

 temperature of the globe. It is pretty generally acknowledged 

 that the average climate of a particular region is not wholly 

 dependant upon the. region's latitude. Islands enjoy a more 

 equable temperature than does land thrown into large masses. 

 It is inferred, therefore, that the relative amounts of heat, 

 received at given times, from the sun may be identically the 

 same, yet that two or more very different climates may 

 prevail. Sir Charles Lyell's theory of climates is well 

 known. " With all the land gai|fcred round the poles," he 

 argues, ''we should experience IKiaximum of cold ; with a 

 preponderance of land at the equator, the reverse conditions 

 would prevail." Geologically this theory is of great practical 

 importance. Very many diverse chmates have, at different 

 times, prevailed upon the earth. Taking from the close of 

 the Cretaceous age, we find that at the dawn of the Tertiary 

 epoch tropical fruits gTCw in what is now England, and that 

 a tropical fauna prevailed whilst our own Victorian Eocene 

 beds were laid down. At a much later period England 

 appears to have been submerged beneath an arctic sea ; its 

 mountains covered with glaciers, and its ocean dotted with 

 icebergs. A little attention will show how these facts bear 

 upon the hypothesis under consideration. As the rate of 

 the earth's axial revolution diminished, the central molten 

 nucleus would be the first portion losing its spheroidity. 

 The rigid crust might, and w^ould, retain its former shape 

 for a lengthened period. There would thus be a hollow 

 beneath the equator, and an increased pressure tending to 

 cause disruptions at either pole ; but for a time this state of 



