76 PROC. COTTESWOLD CLUR vol. xiii. (2) 



between the Eocene mammals and their modern representa- 

 tives are enormous. To take one example. The Eocene 

 horses were about as large as a fox, each front foot was 

 furnished with four toes and a thumb, while the hind feet 

 had three toes, each of them terminating in hoofs. 



We have next to compare the amount of differentiation 

 in Pre-Cambrian times with the differentiation of life in 

 subsequent epochs. We know that at the opening of the 

 Cambrian epoch all, or nearly all, of the existing animal 

 sub-kingdoms had been evolved. These ancient types, as 

 we have seen, must have been differentiated much more 

 slowly than the higher forms. The differentiation before 

 the Cambrian epoch was therefore much greater than 

 since, and it was much less rapid. We are therefore 

 driven to conclude that Pre-Cambrian life took much 

 longer in developing than all the faunas of succeeding 

 epochs. Some authorities make the difference at least 

 nine to one. I will assume it to be one to one. In 

 other words, we may conclude with reasonable certainty 

 that the sedimentary formations — the only ones that are 

 fitted to contain the remains of life — below the Cambrian 

 represent time at least equal to the long succession of 

 epochs represented by the Palaeozoic, Mesozoic, and 

 Kainozoic systems. 



The result at which we have just arrived will appear 

 the more surprising when we reflect upon the paucity of 

 the formations which represent Archaean (Pre-Cambrian) 

 time. Thirty years ago we knew^ next to nothing of these 

 rocks. The Laurentian and the Huronian had been 

 described in America; and the Laurentian had been 

 correlated by British geologists with the crystalline rocks 

 of the Malvern Hills and North-Western Scotland. But 

 since that time the enormous gap between these ancient 

 gneisses and the base of the Cambrian has been partly 

 bridged over by two great formations. First of all, Dr Hicks 



