Cxii PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [May I QOQ, 



On a review of all the facts, the most probable estimate of the 

 age of the Ocean would appear to lie between 80 and 150 millions 

 of years. 



We may now pass from the age of the Ocean to the age of the 

 sedimentary rocks. 



I have previously given on another occasion a table showing the 

 maximum thickness of each of the stratigraphical systems ; I am 

 now able to amend it, thanks to additional information afforded by 

 Chamberlin & Salisbury 1 in respect to some of these systems 

 chiefly as developed in the United States. 



A.D. 1900. A.D. 1909. 

 Feet. Feet. 



Recent and Pleistocene 4000 4000 



Pliocene 5000 13000 



Miocene 9000 14000 



Oligocene 12000 12000 



Eocene 12000 20000 



■ 63,800 



Upper Cretaceous r 24000 



Lower do 14000 120000 



Jurassic 8000 8000 



Trias 13000 17000 



69,000 



Permian 12000 12000 



Carboniferous 24000 29000 



Devonian 22000 22000 



163,000 



Silurian 15000 15000 



Ordovician 17000 17000 



Cambrian 16000 26000 



58,000 



Keweenawan 50000(?) 50000(?) 



Animikian 14000 14000 



Huronian 18000 18000 



82,000 



Archaean ? ? 



Total 33 5,800 feet. 



On comparing the two columns it will be seen that the chief 

 increase in thickness is confined to the Cambrian, the Cretaceous, 

 and some of the Tertiary systems : the thickness of the Jurassic, 

 although very disproportionate to the importance of that system, 

 remains unchanged. It is to be hoped that some future discovery 

 may diminish this anomaly. 



The total thickness amounts to 335,800 feet, and if this accumu- 

 lated at the rate of one foot in a century, the duration of strati- 

 graphical time would amount to more than thirty-three and a half 

 1 T. C. Chamberlin & R. D. Salisbury, ' Geology ' London, 1906. 



