THE DAWN OF LIFE 171 



It is much more likely that the serpentine of 

 the Laurentian limestones was produced in these 

 ways than that it resulted from the hydration of 

 magnesian minerals after the rock was consolidated. 

 In the former case it would be in the most favour- 

 able conditions for mineralizing organisms as glau- 

 conites do in the modern seas. In the latter it 

 would cause disturbances and changes of volume 

 of which we have no evidence. 



We thus find that the chemistry of the modern 

 seas and that relating to the preservation of fossils 

 of various ages by silicious infiltrations lends great 

 probability to the belief that serpentine played 

 this role in the oldest seas, though it would seem 

 that dolomite was more suitable to the filling of 

 the extremities of the minute tubes and their finer 

 terminations.^ 



(3) Our third question leads to the inquiry in 

 what modern or ancient marine animals we can 

 find structures akin to those of our supposed 



* I have shown also that in the limestone containing Eozoon 

 we find layers holding concretions of serpentine alternating 

 with others holding crystals of dolomite, as if there were at 

 some times conditions favourable to the deposition of silicate 

 of magnesia, and at others to that of the carbonate. 



