324 IPo B t e I 6 ia 



mentation in these groups with a concept of the 

 time relations involved in their accumulation. 

 Certain cycles of deposition were observed which 

 in the discussion were associated with the pre- 

 cession of the ecjuinoxes, or a time interval of 

 21,000 years. With a cycle of sedimentation 

 averaging 4 feet in thickness correlating with 

 the precession-perihelion cycle of time, the ac- 

 cumulation of 3,900 feet of usually argillaceous 

 shales involves a period of 20,000,000 years. 

 Assuming the ])rocess of sedimentation to have 

 gone forward at the same rate, when the Port 

 Renfrew series was dey^osited, the time involved 

 could not liave been much less than seventy- 

 seven million years! And a vast accumulation 

 of sediment had taken place before the Pro- 

 vidence Cove beds were formed, as can be seen 

 along the shore for some miles to the east of 

 this inlet. So millions of years more must be 

 added to complete the time necessary for the 

 entire formation. 



Deposition of the sediment is only a part of 

 the process of rock-making. The laminated 

 habit was imprinted when the particles were laid 



