346 THE PHYSICAL GEOGIixVrilY OF THr: SEA. 



teorologj a single well-established fact that is inconsistent with 

 the theory of a crossing at the calm belts. 



645. The geological record affords evidence that the climates 

 Cataclysms. of the earth were once very different from what they 

 are now ; that at one time intertropical climates extended far up 

 toward the north ; at another time polar climates reached, with 

 their icebergs and their drift, far down toward the equator ; that 

 in remote ages most of what we now call dry land was covered 

 with water, for we find on the mountains and far away in the in- 

 terior of continents deposits many feet thick, consisting of sea> 

 shells, marine animals, and organic productions of many sorts. 

 These fossils, marks, and traces indicate that since their day ages 

 inconceivably great have elapsed. Not only so : the lines of drift, 

 and boulders, and gashes with which the earth is scored and strew- 

 ed, afford reason for the conjecture that there have been cata- 

 clysms, in which the waters have swept from north to south, and 

 again from south to north, bearing with them icebergs, huge blocks 

 of stone, rubble, drift, and sediment of various sorts. Lieutenant 

 J alien, M. Le lion, and M. Adhemar have, with marked ability, 

 treated of this subject. They maintain that our earth has a "secu- 

 lar" as well as an annual summer and winter; that these "secular" 

 seasons depend upon the precession of the equinoxes, and that the 

 length of each is consequently 10,500 of our years; and that it is 

 the melting of the polar ices in the "secular" season of one hemi- 

 sphere, and their recongelation in the "secular" winter of the other, 

 that causes a rush of the sea from one hemisphere into the other; 

 and so cataclysms are produced at regular intervals of 10,500 years. 

 In consequence of the inclination of the axis of the earth to the 

 plane of its orbit, we have our change of seasons ; and in conse- 

 quence of the ellipticity of that orbit, the spring and summer of 

 our hemisphere are at present longer than those of the southern. 

 During the excess of time that the sun tarries on our side of the 

 equator, the southern nights are prolonged, so that the night of 

 the south pole — the antarctic winter — is annually a week longer 

 (§ 366) than the arctic. Thus, during the period of 10,500 years, 

 the antarctic regions will experience 142 years of night, or win- 

 ter, in the aggregate, more than the arctic. Therefore it is manir 

 fest, say the catach/sma lists, that, though the two hemispheres do 

 receive annually the same amount of solar heat, yet the amount 



