366 ON THE MOVEMENTS OF THE EARTH's CEUST. 



Miocene. 



From 1,160,000 to 700,000 years before tb^e present time. 



Arc 8'. Etiige Aquitauieu ? 



9'. Etage Langliieu. 



10'. Etage Helvetien. 



11'. Etage Tortonien. 



11'. Etage Messiuieu. 



Pliocene. 



From 700,000 to 350,000 years before the present time. 



Arc 13'. Etage Mated m. 



14'. Etage Plaisancien 



15'. Etage Astien. 



16'. Etage Aruiisien. 



QUATERNARY.— Cycle III." 

 From 350,000 years ago, to the present time. 



Arcs l"-3". Etage Saharien, with three oscillations. 



The limits between the cycles of the curve are not drawn arbitrarily. 

 The beginning and the close of the first two cycles are distinguished by 

 their unusually low eccentricity. The last arc in one cycle and the first 

 in the following one have together a duration of about 150,000 years ; 

 and in all this time the eccentricity was very low. In these two cycles, 

 likewise, the highest mean eccentricity occurs in the middle of the 

 cycle. 



The Eocene period seems to have had sixteen oscillations, and should 

 correspond to the first cycle; the Oligocene, Miocene, and Pliocene 

 have likewise together sixteen oscillations, and correspond to the sec- 

 ond cycle. The Lower Eocene corresponds to arcs 1 to 6, the Middle 

 Eocene to 7 to 12, and the Upper Eocene to 13 to 16. In the same way 

 the Oligocene corresponds to arcs l'-7', the Miocene to 8'-12', and the 

 Pliocene to 13'-16'. There is thus a certain analogy between the older 

 and the younger Tertiary periods. We have here sis divisions which 

 nearly correspond to each other in the following manner: 



Lower Eocene to the Oligocene : the former with six, the latter 



with seven oscillations. 

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



with five oscillations. 

 Upper Eocene to the Pliocene : both with four 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 



*The lower line of curves iu the diagram. 



