RELATIONS OF AIR AND WATER TO TEMPERATURE AND LIFE. 269 



it is 1,500 miles long and about 2,000 miles wide, the largest and rich- 

 est valley of the temperate zone. 



A very low and narrow divide separates the Mississippi Valley from 

 another great valley extending from the Kocky Mountains eastward, 

 with a gentle slope to Hudson Bay and the Atlantic. It is as long 

 from west to east as the valley of the Mississippi is from north to south, 

 and is from 500 to 600 miles wide. The western portion of this plain 

 is drained by Saskatchewan Kiver. The winds which blow over this 

 valley from the Rocky Mountains in some years water imperfectly the 

 western portion of this plain, but with a copious rain-fall the land yields 

 abundantly; the eastern portion is watered from Hudson Bay, lakes 

 Winnipeg, Manitoba, and the other large lakes of that province. As 

 the climate is cold, less rainfall is required than in the valley of the 

 Mississippi. 



Another very low divide separates this valley from the great plain, 

 2,500 miles long, descending with a gentle slope to the Arctic Ocean, 

 through which runs the Mackenzie River. The winds that blow from 

 the Arctic Ocean fall in rain and snow in this valley. 



Thus, through the center of America, from the Arctic to the Antar- 

 tic Oceans, there are no high elevations, while there is a more uniform 

 distribution of rain-fall and temperature than on any other continent. 



From the Arctic Ocean cold currents of water flow along both the 

 eastern and western coasts of Greenland and bear immense icebergs 

 aiul fields of ice southward until they meet the warm waters of the 

 Gulf Stream, when the ice melts, causing fog banks and depositing the 

 debris brought from the Arctic glaciers, thus aiding in the making of 

 the great fishing banks of Newfoundland. The Arctic current, still 

 cold, runs southward inshore from the Gulf Stream, and affects the cli- 

 mate of North America to the latitude of New York if not to Cape 

 Hatteras. 



From the Caribbean Sea and the Gulf of Mexico the Gulf Stream 

 passes around Florida and flows along the southern Atlantic States. 

 The currents of air from the Gulf Stream blow over slightly cooler 

 waters and deposit rain on the eastern side of the Alleghanies and 

 water the eastern coast of the United States. 



EUROPE. 



The main Gulf Stream is deflected, by the shape of the ocean bottom 

 and the contour of North America, northward and eastward toward 

 Europe; but its drift is largely increased by the winds. The drift from 

 the southward sets around the North Cape of Norway, 71^^ north lati- 

 tude, keeping the coast free from ice all the year round, and is felt in 

 the Kara Sea. It is by means of this current that Nansen hopes to 

 be borne through the Kara Sea and from the Lena Delta by way of the 

 north pole to Greenland. 



The winds that blow over the Gulf Stream water the western coast 



