72 RELICS OF PRIMEVAL LIFE 



different from those of any later rocks, and incom- 

 patible with the existence of life. The upper part 

 of the Lauren tian system, however, known in 

 Canada as the " Grenville Series," shows evidence 

 of ordinary marine deposition in quiet waters, which 

 may have been not unfavourable to the lower 

 forms of marine life ; and though its beds have 

 been greatly changed by heat and pressure, we can 

 still to some extent realize the conditions of a time 

 of comparative quiescence intervening between the 

 underlying Lower Laurentian and the succeeding 

 Huronian. This part of the system still contains 

 gneisses, bedded diorites, and other rocks which 

 may have been volcanic ; but it has also quartzites 

 and quartzose gneisses which must have been sand- 

 stones or shales, thick limestones, beds of carbon 

 now in the state of graphite or plumbago, and large 

 beds of iron ore. Such rocks were in all succeed- 

 ing formations produced under water and by accu- 

 mulations of the remains of plants and the hard 

 parts of animals, in strictly sedimentary beds, 

 usually formed slowly and without mechanical 

 disturbance. Hence we may infer that aquatic life 

 at least existed in this early period, and as there 

 must have been land and water, shallows and deep 



