PREFACE IX 



matter of serious work, and that their presentation in 

 this form may stimulate further research in a field 

 which is destined in the coming years to add new and 

 important domains to the knowledge of life in the early 

 history of the earth. 



Hypotheses respecting the introduction and develop- 

 ment of life are sufficiently plentiful ; but the most 

 scientific method of dealing with such questions is that 

 of searching carefully for the earliest remains of living 

 beings which have been preserved to us in the rocky 

 storehouses of the earth. 



There are many earnest labourers in this difficult 

 field, and it will be the object of the writer in the 

 following pages to do justice to their work as far as 

 known to him, as well as to state his own results. 



J. W. D. 



