FROM THE TERTIARY DEPOSITS OF TASMANIA. 347 



and snow and months of darkness did not exist in the Arctic regions. 

 Contemporaneously a corresponding genial climate existed in the 

 southern hemisphere. It is perfectly certain that, under the existing 

 astronomical arrangements, there must be prolonged day and pro- 

 longed night at the poles and for a certain number of degrees in the 

 equatorial direction ; and the inclination of the polar axis to the 

 plane of the ecliptic necessitates the perpetuation of the present arctic 

 and antarctic climates. The astronomical conditions under which 

 a sufficient amount of light could be given to the plants within twenty 

 degrees of the pole are not those which now prevail; but were the polar 

 axis at right angles to the plane of the ecliptic, and were there no 

 greater node than at present, there would be equal day and equal 

 night. The biologist claims this as the earliest position of the globe. 

 The arguments against such an inference relate, of course, to the 

 nature of the forces which could bring down the north pole, or rather 

 which would incline the polar axis, and to the amount of solar heat 

 which would reach the polar regions. Probably no force acting on 

 the globe as a mass, such as gravitational energy, could alter the 

 position of the poles as they are now, with reference to the ecliptic ; 

 for after a very slight inclination had been produced, the force 

 would produce no more obliquity, but only a more or less rapid pre- 

 cessional movement. 



Nor is it possible to understand how any external force could cause 

 the approach of one pole to the sun and the recession of the other, 

 the globe being comparatively homogeneous, for the sake of argu- 

 ment, and the polar axis being supposed to be at right angles to the 

 plane of the ecliptic. 



But it would be possible if a vast alteration in the relative distri- 

 bution of land and sea occurred, in one hemisphere especially. It 

 is perfectly reasonable to infer that the great subsidences of the 

 Miocene lands, and the formation of the Southern Ocean, whose 

 area is greater than that of all the land to the north, and the vast 

 upheaval of the Central- Asian, Caucasian, and Alpine and other 

 areas, producing great alterations in the homogeneous condition, 

 brought the land-surfaces of the north with their higher specific gra- 

 vity and great mass within the influence of the gravitational energy 

 of the sun. From that time dated the long winter's night and the 

 presence of perpetual ice and frost in the highest latitudes ; and 

 those changes in the climatal conditions of the northern and southern 

 areas, where reef-corals had built and the light-requiring floras had 

 flourished. The objection regarding the small amount of heat 

 which would be granted to the high latitudes under the conditions of 

 a vertical polar axis are of the nature of those which sadly troubled 

 our science with respect to the impossibility of animals living at 

 very great depths in the sea in consequence of the pressure to 

 which they would have to submit, and to the warm temperatures 

 which must prevail in the oceanic abyss. 



The presence of land in the extreme north or south on which no 

 perpetual ice rested except on the high hills, would introduce an ele- 

 ment into the argument which would suffice to demonstrate a tem- 



Q. J. G. S. No. 127. 2 b 



