114 



THE DAWN OF LIFE. 



the Laurentian country. Perliaps where vegetable 

 matter was very abundant Eozoon did not thrive, or 

 on the other hand the growth of Eozoon may have 

 diminished the quantity of vegetable matter. It is 

 also to be observed that much compression and distor- 

 tion have occurred in the beds of Laurentian limestone 

 and their contained fossil s^ and also that the specimens 

 .are often broken by faults^ some of which are so small 

 as to appear only on microscopic examination, and to 

 shift the plates of the fossil just as if they were beds of 

 rock. This, though it sometimes produces puzzling 

 appearances, is an evidence that the fossils were hard 

 and brittle when this faulting took place, and is conse- 

 quently an additional proof of their extraneous origin. 

 In some specimens it would seem that the lower and 

 older part of the fossil had been wholly converted into 

 serpentine or pyroxene, or had so nearly experienced 

 this change that only small parts of the calcareous wall 

 can be recognised. These portions correspond with 

 fossil woods altogether silicified, not only by the filling 

 of the cells, but also by the conversion of the walls 

 into siHca. I have specimens which manifestly show 

 the transition from the ordinary condition of filling 

 with serpentine to one in which the cell-walls are 

 represented obscurely by one shade of this mineral 

 and the cavities by another. 



The above considerations as to mode of preservation 

 of Eozoon concur with those in previous chapters in 

 showing its oceanic character ; but the ocean of the 

 Eozoio period may not have been so deep as at 



