^32 PKKSIUKNTS ADDliKSS. 



rci'nis is not sutficient to account for the difiference between the 

 existing sea-level and the horizon of very many deposits of marine 

 strata, it is quite probable, as has been already indicated, that 

 considerable fluctuations in the quantity of ice stored at the poles 

 may have taken place, and that some of the minor mutations in 

 ocean level, which have left records behind, may have been due 

 to this cause. 



The existence of fossils of various kinds i/i siiii in the polar 

 regions proves that at some period in the past the climate in 

 these places must have been ver^^ much warmer than is now the 

 case. Now there are very great physical difficulties in the 

 way of any change in the position of the world relative to 

 the sun, which would cause any material alteration in the situation 

 of the polar ice-caps. In fact, short of a catastrophaic occurrence 

 quite out of the orderly sequence of events, there does not seem 

 any possibility of such a change taking place. The total variation 

 of polar position relative to the sun, caused by the precession of 

 the equinoxes — an event occupying about 26,000 years— is much 

 too small to have so great an effect, even when the period of 

 greatest displacement of the earth's poles is made to coincide 

 with the most favourable position of the earth in its orbit, 

 relative to the sun. By a catastrophaic occuirence is to 

 be understood such an event as the impact of a gigantic 

 meteorite, sufficient to upset the equilibrium of the earth 

 and materially alter its centre of gravity. While it is by no 

 means impossible or even improbable that such an event may 

 have taken place, we have no direct evidence thereof, and there 

 is little doubt that collision with a body sufficiently large to 

 induce so great a change would result in the liberation of an 

 amount of heat that would instantly destroy all life on the globe. 

 Certainly there are in particular spots on the earth's surface 

 great masses of iron, which are usually considered to be of 

 meteoric origin, but it may well be doubted if the impact of these 

 would be sufficiently severe to produce the change in position in 

 question. It has been suggested that, as the world in the 

 first instance gradually cooled from its pristine molten condition, 



