288 



LAURENTIAN SYSTEM OF ROCKS AND ARCHAEAN ERA. 



Time represented. — The enormous thickness of these rocks (50,000 

 feet in Canada, and still greater in Bohemia and Bavaria) certainly in- 

 dicates a very great lapse of time. It is probable that the Archaean 

 era is longer than all the rest of the recorded history of the earth put 

 together ; and yet, precisely as in the beginnings of human history, the 

 record is almost a blank. The events are few, and imperfectly recorded. 

 Evidences of Life. — We have already explained (p. 144) how iron- 

 ore is at present accumulated. We have there shown that all accumu- 

 lations of this kind now going on are formed by the agency of organic 

 matter. It is almost certain that the same is true for all times, and 

 therefore that iron-ore accumulations are the sign of the existence of 

 organic matter, and the quantity of the ore accumulated is a measure of 

 the amount of organic matter consumed in doing the work. The im- 

 mense beds of iron-ore found in the Laurentian rocks are, therefore, 

 evidence of the existence of organisms in great abundance. That these 

 organisms were chiefly vegetable, we have the further evidence derived 

 from the great beds of graphite ; for graphite, as we shall see hereafter, 

 is only the extreme term of the metamorphism of coal. 



Of the existence of animal organisms the evidence is not yet com- 

 plete, although it is probable that the lowest forms of Protozoa, such 



as rhizopods, were abun- 

 dant. We have seen that 

 limestones are abundant 

 among the Laurentian 

 rocks. Now, the limestones 

 of subsequent geological 

 epochs are almost wholly 

 composed of the accumula- 

 ted shelly remains of low- 

 er organisms, especially 

 nullipores and coccoliths 

 among plants, and rhizo- 

 pods among animals. 



The existence of rhizo- 

 pods is believed by some to 

 have been demonstrated. 

 There have been found 

 abundantly, in the Lauren- 

 tian limestones of Canada, of Bohemia, of Bavaria, and elsewhere, 

 large, irregular, cellular masses, which are believed by good authorities 

 to be the remains of a gigantic foraminiferous rhizopod. The sup- 

 posed species has been called Eozoon * Ganadense. Fig. 262 is a sec- 



Fig. 262.— Section of the Base of Specimen of EozoOn, 

 x §. From a photograph. (After Prestwich.) 



* Dawn animal. 



