i] HISTORICAL 13 



still another of as many as nine ' Gaeans ' as chief 

 units, and others prefer six zones, to indicate that 

 chaos reigns instead of order. 



Although with this wild search for the true regions 

 the value of the fossil animals became fully recognised 

 as the only absolute evidence of distribution in the 

 past, it was frequently ignored that the various groups 

 of animals have appeared in successive geological 

 epochs and also at many places remote from each 

 other. The key to the distribution of any group lies 

 in the geographical configuration of that epoch in 

 which it made its first appearance ! If, for argu- 

 ment's sake, some group of land animals had come 

 into existence in Africa, when this was still con- 

 tinuous with Madagascar, the present descendants 

 of these animals may well be found in both countries, 

 but this could not be the case with another group 

 which was evolved after Madagascar had become an 

 island. This is so obvious as to sound like a platitude. 



If all the various groups of creatures had come 

 into existence at the same epoch and at the same 

 place, then it would be possible, given sufficient data 

 as to present and past distribution, to construct a 

 map showing the generalised results applicable to 

 the whole animal kingdom. But the premises are 

 wrong. Whatever regions or primary centres we may 

 seek to establish as applicable to all classes, we are 

 necessarily mixing up several principles, namely time 



