英美文化背景与国家概况之美国地理.pptxVIP

White House ; contents(156-162); Satellite map of America 卫星地图中的美国;Topographic map of the United States of America 美国地形图; Land Resource About 47% of America’s land area can be used for agricultural purposes，including 400 million acres of arable（适于耕种的） cropland and 900 million acres of permanent pastureland（牧场）。; The main rivers and mountains of America ;Mississippi River , it flows about 6400 kilometers from its northwestern source in the Rockies to the Gulf of Mexico ,Its tributaries include nearly all the rivers west of the Appalachian mountains(阿帕拉契山脉) and the east of the Rockies .;;;;;;Potomac river(波托马克河) , it is famous not only because Washington D.C ,it is regarded as the traditional dividing line between the South and the North .; The scenery of Potomac river ;;;Great lakes , of these five lakes only one , Lake Michigan , belongs to America completely while the other four are shared with Canada . These five lakes , with an area of about 240000 square kilometers , constitute the largest lake group in the world . ; Great lakes 五大湖; Great lakes 五大湖; Lake superior; Lake Michigan; Lake Huron; Lake Erie; Lake Ontario;Niagara Falls The five lakes slope downward towards the east . Lake Erie is over 100 meters higher than Lake Ontario and the river that connects them is called Niagara（尼亚加拉） River . The steep drop in elevation gives birth to the Niagara Falls , it attracts large numbers of visitors from around the world . ;;;;; America has been known for its rich forest resources . When the first European colonists arrived , America was still covered with dense forests , stretching about 1600 kilometers inland(国内的) from the Atlantic Coastline .Today about one-third of the United States is still covered with forests ; T