THE APPEARANCE OF LIFE ON THE GLOBE 329 



ments of that epoch, of which the texture then 

 remains absolutely the same as those of the most 

 normal primary sediments. Thus it was not long 

 before, in various directions, more or less defined 

 traces of life commenced to be distinguished. First 

 footprints or perforations of problematic animals 

 were discovered in the sandstone of the Scottish 

 Highlands, and found again by Lebesconte in the 

 schists round Rennes. In the same district of 

 Brittany, another French scholar, Cayeux, while 

 examining some narrow cuttings effected in certain 

 pre-Cambrian carboniferous schists, thought he 

 recognized in these preparations some elegant 

 lattice-work spherules, identical with the Silicious 

 shells of certain of our present Radiolaries. He, 

 moreover, described traces therein, rather less 

 denned, it is true, of the shells of Foraminifera and 

 of the spiculse of Sponges. Although the authenti- 

 city of these organisms has given rise to certain 

 controversies, it was impossible not to be struck, 

 at least, by the fact that the simplicity of organiza- 

 tion of these pre-Cambrian animals belonging to 

 the very lowest groups of Invertebrates, answered 

 well enough to the a priori idea which we must 

 conceive of a really primitive fauna. The pre- 

 Cambrian fauna of Brittany certainly possessed the 

 most probable characteristics of an animal world 

 still very near to its own origins. Once again, how- 

 ever, this simple way of regarding the matter had 

 to be abandoned. 



The methodical exploration by the American 

 geologists of the ancient soils of Canada and of the 

 Rocky Mountains reserved for us, indeed, quite un- 



