the Displacement of Shore-lines. 509 



which nearly correspond to each other in the following 

 manner : — 



Lower Eocene to the Oligocene : the former with 6, the 



latter with 7 oscillations. 

 Middle Eocene to the Miocene : the former with 6, the latter 



with 5 oscillations. 

 Upper Eocene to the Pliocene : both with 4 oscillations. 



The great overflows of the sea occur in the middle of the 

 cycles, in the Middle Eocene, the Upper Oligocene, and the 

 Miocene. In the middle of the cycles the mean value of the 

 eccentricity was greatest. At the commencement and the 

 last part of the cycles, when the mean value of the eccentricity 

 was small, the sea retreated far, as between the Cretaceous and 

 the Eocene, and in the Upper Eocene and Pliocene. The 

 notion therefore presents itself with great probability that 

 there is a connexion between the cycles in the curve repre- 

 senting the eccentricity of the earth's orbit and what is called 

 a geological epoch, or what has also been called a " cycle " or 

 " circle of deposition." The two Tertiary cycles are as it 

 were great stages, each composed of 16 smaller ones. Just 

 as each of these 16 represents a small oscillation of the sea, so 

 does each cycle represent a great oscillation ; but this great 

 oscillation has been accomplished by means of the 16 small 

 ones. In the same way the mean value of the eccentricity 

 rises and falls in each cycle with 16 oscillations ; it is low at 

 the commencement of the cycle, attains its greatest value in 

 the middle of the cycle, and falls again towards the close. 

 These agreements between the cycles of the curve and the 

 formations, between the arcs of the curve and the stages, and 

 between the number of the arcs' precessions and the alterna- 

 tions of the strata in the stages wherever these could be 

 checked, appear to me to be so striking as to exclude the 

 notion of an accidental coincidence, and distinctly point to a 

 causal relation. 



If we would test the correctness of our hypotheses by 

 means of the older formations, the following points must 

 be borne in mind: — After investigating the laws of the varia- 

 tions of eccentricity, Geelmuyden told me that it is probable 

 that a cycle of about 1,500,000 years must appear in the 

 curve, but that without more extended investigation we can- 

 not conclude that this will continue unchanged for unlimited 

 periods. Even in the calculated curve the Cycle III. is 

 distinguished from the other two by a much lower eccentricity 

 in the arcs A"-^". 



If the polar compression in old times was greater, then tho 

 Fhil. Mag. S. 5. Vol. 27. No. 169. June 1889. 2 M 



