SEA ROUTES, CALM BELTS, AND VARIABLE WINDS. 347 



from the north-east trade-wind air ; the latter, therefore, after 

 rising np, is the cooler and the more compact ; and as, by the 

 theory of the crossings, it flows off to the south as an tipper 

 current, it presses upon the barometer with more weight than 

 the warmer and more moist air that feeds the current which is 

 above and counter to the north-east trades. There is not in the 

 whole range of marine meteorology a single well-established 

 fact that is inconsistent with the theory of a crossing at the calm 

 belts. 



645. Cataclysms. — The geological record affords evidence that 

 the climates of the earth were once very dififerent from what 

 they are now; that at one time intertropical climates extended 

 far up towards the north ; at another time polar climates reached, 

 with their icebergs and their drift, far down towards 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 interior of continents deposits many feet thick, con- 

 sisting 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 strewed, afibrd reason for the conjecture that there 

 have been cataclysms, in which the waters have swept from north 

 to south, and again from south to north, bearing with them ice- 

 bergs, huge blocks of stone, rubble, drift, and sediment of various 

 sorts. Lieutenant Julien, M. Le Hon, and M. Adhemar have, 

 with much ingenuity, treated of this subject. They maintain 

 that our earth has a " secular" as well as an annual summer and 

 winter; that these "secular" seasons depend upon the pre- 

 cession of the equinoxes, and that the length of each is con- 

 sequently 10,500 of our years ; and that it is the melting of the 

 polar ices in the " secular" season of one hemisphere, 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 



