24 REPORT— 1886. 



Arctic cnrrentE and tbe d.'eenland ice is sufficient to permit icebergs 

 "which creep down to the mouth of the Strait of Belle Isle, in the latitude 

 of the south of England, to remain unmelted till the snows of a succeed- 

 ing 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 tc 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 

 quantities of it would remain undissolved in summer, and thus an accu- 

 mulation 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 America and 

 Europe might become uninhabitable, except by arctic animals and plrnts, 

 as far south as perhaps 40° of north latitude. This would be simply a 

 return of the Glacial age. I have assumed only one geographical change ; 

 but other and more complete changes of bcj^sidence and elevation might 

 take place, with effects on climate still more decisive ; more especially 

 would this be the case if there were a considerable submergence of the 

 land in temperate latitiides. 



We may suppose an opposite case. The high plateau of Greenland 

 migh', subside or be reduced in height, and the openings of Baffin'" 3ay 

 and the North Atlantic might be closed. At the same time the interior 

 plain of America might be depressed, so that, as we know to have been 

 the case in the Cretaceous period, the warm waters of the Mexican Gulf 

 would circulate as far north as the basins of the present great American 

 lakes. In these circumstances there would be an immense diminution of 

 the sources of floating ice, and a correspondingly vast increase in the sur- 

 face of warm water. The effects would be to enable a temperate flora to 

 subsist in Greenland, and to bring all the present temperate regions of 

 Europe and America into a condition of subtropical verdure. 



It is only necessar/ to add that we know that vicissitudes not dis- 

 similar from those aboTe sketched have actually occurred in compara- 

 tively recent geological times, to enable us to perceive that we can dis- 

 pense with all other causes of change of climate, though admitting that 

 some of them may have occupied a secondary place.'* This will give us 

 in dealing with the distribution of life the great advantage of not being 



• According to Bonney, the west coast of Wales is about 12° above the average for 

 its latitude, and if reduced to 12" below the average its mountains would have large 

 glaciers. 



* More especially the ingenious and elaborate arguments of CroU deserve con- 

 sideration ; and, though I cannot agree with him in his Qtain thesis, I gladiy acknow- 

 ledge the great utility of the work he has done. 



