DKKT-sKA i:xri.<>i;.M I<>.\. 159 



appear in tin- (JfillOt" Mcxii". lUit, exclusive of these, 

 wliicli probably jtiojcct Irom a (.oinparativoly oven slope, 

 tiio topo«?rai)hy of the sea-bed in deep water is carved in 

 broad and easy curves, which lind no parallel on land. 

 This results from the absence of denudation in the sea. On 

 the land, torrents, storms, rivers, winds, all modify the sur- 

 face, which must have originally been much like that of 

 the sea-beil. (Jullies.f avines, terraces, sharit-weathered rock 

 face.s, peaks, and jiinnacles, are formed in air by the denud- 

 ing agencies. In the dee]) sea there can be no sharply limited 

 currents or denuding agencies. Such currents as may exist 

 will have ill-dehned margins, will move at slow rates, and 

 cannot be conceived of as ploughing sharp grooves or gullies 

 in the floor of ocean. It is probable that the very deep sea 

 is for the most part a region of profound quiet, where the 

 waters are and remain unmoved, either by the compara- 

 tively superficial ocean currents and tides, or the pulses of 

 the waves as they beat on distant shores. The great deeps 

 which you see represented on this model and in the chart 

 of the Atlantic sea-bed here exhibited are not paralleled 

 by anything on dry land, except the basins of the Great 

 Lakes. Were they above the sea they would become lakes 

 at once, and would gradually be filled by sediments. Their 

 existence here in the deep sea disposes of the hypothesis 

 rashly advanced by some glacialists, that great lake basins 

 are due only to the action of glaciers; and that without the 

 previous existence of land-ice there \vould be no large lakes 

 on the earth's surface. It would be a bold man who would 

 l>ropose to locate glaciers on the bottom <>f tb.. r.nlf of 

 ^h'xico. 



The circulation of the waters in the sea has been ihco- 

 retically accounted for by differences of density due to 

 evaporation and consequent over-salt ness, and to differences 

 of temperature between the water at the poles and at the 

 equator. This theoretical circulation doubtless exi.sts in a 

 more or less modified form, and allects the actual motion of 

 the waters. F>ut tlir existing oceanic circulation in its 

 greatest part is due directly to the influence of the trade- 

 winds, and is, comparativ) Iv -iMakiiii:. superficial. 



