PREFACE 



TT IS now more than thirty-five years since the 

 announcement was made of the discovery of 

 remains supposed to indicate the existence of animal 

 life in the oldest rocks known to geologists. It was 

 hailed with enthusiasm by some as " opening a new 

 era in geological science " ; but was regarded with 

 scepticism by others, in consequence of the condition 

 and mineral character of the supposed fossil, and be- 

 cause of the great interval in time between the oldest 

 animal remains previously known and these new 

 claimants for recognition. Since that time, many new 

 facts have been learned, and the question has been 

 under almost continuous discussion and debate, with 

 various fortunes, in different quarters. 



