SEA ROUTES, CALM BELTS, AND VARIABLE WINDS. 333 



air wMcli the north-east trade-winds dehver into the calm belt is 

 not as heavily laden with moisture as that of the south-east trades. 

 It is not as heavily laden for two reasons ; one is, the south-east 

 trade-^vind belt is broader than the north-east; consequently, in 

 the former there is more air in contact with the evaporating sur- 

 face. In the next place, the north-east trade-wind belt includes 

 more land within it than the south-east ; consequently, when the 

 two winds arrive at the calm belt, they are, for this reason, also 

 unequally charged mth moisture. Now, when they rise up and 

 precipitate tliis moisture, more heat is liberated from the south- 

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

 after rising up, is the cooler and the more compact ; and as, by the 

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

 it presses upon the barometer ^^dth more weight than the warmer 

 and more moist au' 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. The geological record affords evidence that the climates 

 Cataclysms. of the cartli wcro once very different from what they 

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

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

 theu' 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 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 strewed, 

 afford 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 icebergs, huge blocks of 

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

 Juhen, M. Le Hon, and M. Adhemar have, with much ingenuity, 

 treated of tins 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, 



