PROBABILITIES AS TO LAURENTIAN LIFE, AND 

 CONDITIONS OF ITS PRESERVATION 



\T /"E have seen that the mineral constitution of 

 the Upper Laurentian affords evidence that 

 in this age there were already land and water, and 

 that the processes by which the land is being worn 

 down, and its materials deposited on the sea-bottom, 

 were in full operation ; while the absence of any 

 evidence of violent wave-action, and the presence of 

 thick deposits of limestone, coaly matter, iron ore, 

 and fine-grained beds of sediment, indicates a time 

 of rest and quiescence. All these conditions were 

 favourable to the presence of life, and we should 

 expect to find in such a period some sign of its 

 commencement. 



But here we are met by a formidable difficulty. 

 If the beds of the Grenville series were originally 

 deposits in a quiet sea, they are, as now existing in 

 the old Laurentian hills and valleys, very much 

 changed from their original condition. They have, 



