CONTEMPORAEIES AND SUCCESSORS OF EOZOON. 129 



I^Hnplest kinds of protozoa predominated over all other 

 ^^■rtns of life; but this impression would at once be 

 corrected by the examination of other deposits of the 

 same age : so our inferences as to the life of the Lau- 

 rentian from the contents of its oceanic limestones 

 may be very imperfect, and it may yet yield other and 

 various fossils. Its possibilities are, however, limited 

 by the fact that before we reach this great depth in 

 the earth^s crust, we have already left behind in much 

 iwer formations all traces of animal life except a few 

 of the lower forms of aquatic invertebrates ; so that we 

 are not surprised to find only a limited number of 

 living things, and those of very low type. Do we 

 then know in the Laurentian even a few distinct 

 species, or is our view limited altogether to Eozoon 

 Canadense ? In answering this question we must bear 

 in mind that the Laurentian itself was of vast dura- 

 tion, and that important changes of life may have 

 taken place even between the deposition of the Eozoon 

 limestones and that of those rocks in which we find 

 the comparatively rich fauna of the Primordial age. 

 This subject was discussed by the writer as early as 

 1 865, and I may repeat here what could be said in 

 relation to it at that time : — 



^^In connection with these remarkable remains, it 

 appeared desirable to ascertain, if possible, what share 

 these or other organic structures may have had in the 

 accumulation of the limestones of the Laurentian 

 series. Specimens were therefore selected by Sir W. 

 E. Logan, and slices were prepared under his direc- 



K 



