Postelsia 
(SS) 
to 
fs 
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 equinoxes, 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 process of sedimentation to have 
gone forward at the. same rate, when the Port 
Renfrew series was deposited, the time involved 
could not have 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 
