msTOinCAL XOTICKS. 9 



llic winds, (l('|i('ii(liii)4 nn the cjiitirs tciiijicraLiiic atid 

 rotation. Tlu' couisfs of the ciirrt'iils ai'c also constant, 

 t'xccpt in so far as inodilicd l»y coasts and lianUs: and the 

 direction of the drift -sci'atclics and transport of hoiddcrs 

 in the rieistoeene l>n|ii nf l'lnro|te ami Anunaca, show tliat 

 tlie aretii' cnricnls a! least, have remained nnchan.i^cMl. 

 I»ut the distrihiil i<ai of laud and water is a \ariai»h' 

 elcnuMit, since we lumw thai in the |H!riod in ([nesiion 

 nearly all northern l'!uro|te, Asia and America were at 

 oiM' time i)V another nmler tht! waters of the s(vi, and it is 

 consi'(|nently to tiiis cause that we must mainly look for 

 the chann'cs wliieli have oeeuri'e(l. 



"Such chan,L!,es of level must, as lias heeii lon;^ since 

 shown hy Sir Charles Lyidl, modify and chan,u;e (diniate. 

 EveiT diminution of the land in arctics Ameiica must 

 tend ti» rendei' its (diniate less severe. l^iVery diniinutiou 

 of land in the t(un|K!rat(! re,yions nmst tend to reduce 

 IJK^ m(sin tiMuperat nre. Kvery diminution of land aiiy- 

 wIku'c! nmst lend to diminish tlu^ extremes of luuit 

 aiulcold; and the condition of tlui southern hennsphere 

 at present shows that the suhmert^'cuu'e of the ^ruat 

 continental masses would lowcu- the mean temperature, 

 hut render the climate much less extreme. (Jlaeiers 

 mii^hl then exist in latitudes wluu'e now the summer heat 

 would suMice to melt them, as Darwin has shown that in 

 vSouth America glaciers extend to the sea level in latitude 

 46° 50'; and at the same time the ice would melt more 

 v«lowly and he drifted farther to the southward. [In the 

 southern hemis[)here, indeed, a glacial period of a peculiar 

 kind exists at present, since there is ati ice -hound 

 antarctic continent 1^,000 miles in diameter and houlder- 

 drift extending from it half-way to the eipiator.] Any 

 change that tended to divert the arctic currents from our 



