GEOLOGY OF THE ATLANTIC OCEAN. 185 



by the winds, and the influence so transmitted is rather in the nature 

 of a disturbing than of an equalizing cause. It follows that any 

 change in the distribution of land and water must affect climate, 

 more especially if it changes the character or course of the ocean- 

 currents. 



At the present time the North Atlantic presents some very pe- 

 culiar and, in some respects, exceptional features, which are most 

 instructive with reference to its past history. The great internal 

 plateau of the American Continent is now dry land ; the passage 

 across Central America between the Atlantic and Pacific is blocked ; the 

 Atlantic opens very widely to the north ; the high mass of Greenland 

 towers in its northern part. The effects are that the great equatorial 

 current running across from Africa and embayed in the Gulf of Mexi- 

 co is thrown northward and eastward in the Gulf Stream, acting as a 

 hot-water apparatus to heat up to an exceptional degree the western 

 coast of Europe. On the other hand, the cold Arctic current from 

 the polar seas is thrown to the westward, and runs down from Green- 

 land past the American shore. The pilot chart for June of this year 

 shows vast fields of drift-ice on the western side of the Atlantic as 

 far south as the latitude of 40°. So far, therefore, the glacial age in 

 that part of the Atlantic still extends ; this at a time when, on the 

 eastern side of the ocean, the culture of cereals reaches in Norway 

 beyond the Arctic Circle. 



Let us inquire into some of the details of these phenomena. The 

 warm water thrown into the North Atlantic not only increases the 

 temperature of its whole waters, but gives an exceptionally mild cli- 

 mate to Western Europe. Still, the countervailing influence of the 

 Arctic currents and the Greenland ice is sufficient to permit icebergs 

 which creep down to the mouth of the Strait of Belle Isle, in the lati- 

 tude of the south of England, to remain unmelted till the snows of a 

 succeeding winter fall upon them. 



Now let us suppose that a subsidence of land in tropical America 

 were to allow the equatorial current to pass through into the Pacific. 

 The effect would at once be to reduce the temperature of Norway and 

 Britain to that of Greenland and Labrador at present, while the latter 

 countries would themselves become colder. The northern ice, drifting 

 down into the Atlantic, would not, as now, be melted rapidly by the 

 warm water which it meets in the Gulf Stream. Much larger quan- 

 tities of it would remain undissolved in summer, and thus an accumu- 

 lation of permanent ice would take place, along the American coast at 

 first, but probably at length even on the European side. This would 

 still further chill the atmosphere, glaciers would be established on all 

 the mountains of temperate Europe and America, the summer would 

 be kept cold by melting ice and snow, and at length all Eastern Ameri- 

 ca and Europe might become uninhabitable, except by Arctic animals 

 and plants as far south as, perhaps, 40° of north latitude. 



