62 A. BLYTT. [NO. 1. 



representing the eccentricity of the Earth's orbit and what is 

 called a geological epoch, or as it has also been called a „ cycle' 1 

 or „circle of deposition." The two Tertiary cycles resemble 

 great stages that are each composed of 16 small ones. Just as 

 each of these 16 small stages represents a slight oscillation of 

 the sea, so does each cycle represent a great oscillation; but 

 that great oscillation has been contained in, and completed itself 

 through, the 16 smaller ones. In the same way the mean value 

 of the eccentricity rises and falls in each cycle with 16 oscilla- 

 tions. It is low at the beginning of the cycle, it attains it 

 greatest value in the middle of the cycle, and sinks again to- 

 wards the close of the cycle. The agreements between the cycles 

 of the curve and the epochs, between the arcs of the curve and 

 the stages, and between the number of the arc's precessions 

 and the alternations of the strata in the stages, wherever they 

 could be controlled, appear, to me, to be so striking that they 

 exclude the thought of an accidental coincidence, and distinctly 

 point to a cause and effect relationship. 



If we would attempt to test the correctness of the hypo- 

 theses I have presented, with the aid of the older formations, 

 then we must bear in mind the following. Geehmnidm has. after 

 investigating the laws regulating the changes in the eccentricity, 

 stated to me that it is likely that a cycle of about 1.500,000 

 years must appear in the curve; but we cannot without more 

 extended investigation conclude that it will continue unchanged 

 . during unlimited periods. Even in the calculated curve the 

 cycle III distinguishes itself from the two others by a much 

 lower eccentricity in the arcs 4" to 9". 



If the Earth's oblateness in ancient times was greater, then 

 the period of precession was also shorter. It would (cfr. Geetr 

 muyden) be very nearly proportional to the square of the time of 

 rotation. To a rotation of 16 hours corresponds e. g. a (syuodic) 

 precessional period of 10,000 years, consequently only the half of 

 the present. The shorter the period, the less distinguished (all 

 other things being alike) must the climatic period be, and the 

 more indistinct the alternation of the strata. 



