CXvi PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [May I909, 



to them and raise the final total to 80 millions of years. This 

 we may divide into two moieties or aeons, one pre-Cambrian — 

 the Protseon, the other post-Cambrian — the Hysterseon ; and we 

 may regard one foot of sediment in a continuous series as roughly 

 representing a lapse of one hundred years. This one foot in a 

 century is certainly only a more or less plausible guess, yet it is 

 not likely to be in excess of the truth, as regards the time, which 

 most geologists will, I think, be disposed rather to increase than 

 diminish. 



The absence or rarity of fossils in the Protseonic sediments is 

 still a subject of speculation, especially among those geologists 

 who are most familiar with the Keweenawan System or its equiva- 

 lents. Some of these are of such promising appearance that the 

 observer, when introduced to them for the first time, applies his 

 hammer in the confident expectation of a rich booty, and on 

 reluctantly abandoning the search remains still unconvinced that 

 the fossils are not there. A few stray traces of organisms have 

 indeed rewarded the patience of investigators from time to time, 

 especially in the Belt terrane of western North America. An 

 excellent account of ail that have been discovered is given by 

 Walcott. 1 Aspidella is plainly organic ; and so, very probably, is 

 Beltina, but few geologists will, I imagine, agree in assigning it 

 to the Merostomata without far more convincing evidence than has 

 yet been adduced. 



Dr. Daly 2 attributes the absence of calcareous fossils to a 

 supposed limeless or rather putrid Ocean. A comparison is made 

 with the Black Sea, where, however, the conditions are very 

 different from those which prevail in the open Ocean. The 

 ancestors of the Cambrian fauna must have inhabited the earth 

 during the greater part of the Protseon, and we have no reason to 

 suppose that their evolution was accomplished in an unwholesome 

 environment. 



The quantity of carbonate of lime in the existing Ocean is 

 remarkably small, owing to its constant removal from solution by 

 organisms. Kivers would contribute all that it contains in about 

 five millions of years, that is, during the first eighth of the 

 Protoeon. The presence of thick-valved Unios in ordinary river- 

 water shows that neither the absence of sodium-chloride nor 



1 C. D. Walcott, ' Pre-Carubrian Fossilif'erous Formations ' Bull. Geol. Soc. 

 Am. vol. x (1899) pp. 199-244. 



2 E. A. Daly, ' The Limeless Ocean of Pre-Cambrian Time ' Am. Joum. Sci. 

 ser. 4, vol. xxiii (1907) pp. 93-115. 



