Vol. 65.] AXNIVEESAEY ADDEESS OF THE PEESIDEXT. CXiii 



millions of years, or in round numbers to thirty-four millions. This 

 is very much less than the minimum estimate found for the age of 

 the Ocean, indeed about one-half ; and, since the deposition of sedi- 

 ments must have commenced with the birth of the Ocean, we are 

 at once confronted with a discrepancy which demands our serious 

 attention. It is true that we possess no definite information 

 regarding the rate at which the ancient sediments were accumu- 

 lated, but it seems extremely unlikely that in those places where 

 they attain their maximum thickness the rate can have greatly 

 exceeded that which we have assumed. 



Something, no doubt, will bo set down to our ignorance of the 

 early history of the stratified rocks — the Archooan still remains 

 shrouded in mystery. Ancient systems may have existed which have 

 since disappeared, either wholly or in part, by absorption into the 

 underlying crust. Sederholm believes that he has discovered a whole 

 series of such systems partly destroyed and completely transformed 

 by invading igneous floods, these he names the Ladogian, Bottnian, 

 Upper and Lower Kalevian, Jatulian, and Jotnian, and adds that 

 each is separated from its neighbour by an unconformity. The 

 great Schist Series of North America presents lis with another 

 system, or set of systems, arrested midway in its progress towards 

 destruction. 



Palaeontologists have repeatedly suggested that at least as much 

 time must have elapsed before the Cambrian Period as after it, 

 and a review of the earliest-known fauna might lead us to regard 

 this estimate as not unreasonable. If we represent such a period 

 by feet of sediment, then the pre-Cambrian systems should have 

 originally possessed a thickness of 254,000 feet, and the total 

 duration of stratigraphical time would become fifty-one millions 

 of years. But even this is less than our fourth, and lowest pro- 

 bable, estimate of the age of the Ocean. 



One other source of error may exist. Gaps, not represented by 

 sediment, may occur in the series. The significance of uncon- 

 formities has never been more fully appreciated than it was in the 

 middle of last century, when Ramsay with great insistence called 

 attention to the vast lapse of time which an unconformity involves. 

 In his masterly contribution to the first volume of the memoirs of 

 the Geological Survey, published in 1846, he showed how some 

 20,000 to 30,000 feet of Palaeozoic sediments had been folded up 

 and denuded away before the deposition of the New Eed Sandstone. 

 His conclusions, received with incredulity at the time, have since 

 been relegated to the obvious. 



