292 GEOGRAPHICAL RESEARCH IN THE UNITED STATES 



field of activity is far wider than we have indicated — so wide, 

 indeed, that time will not permit even a mention of details. 



Thus have we briefl}' summarized and characterized the work 

 carried on by the greater geographic agencies of the government 

 of the United States ; and yet such summary would be incom- 

 plete wdthout mention at least of several other agencies still at 

 work and actively contributing to a fuller and better knowl- 

 edge of our geography. 



The total railroad mileage of the United States, not counting 

 second or third tracks or sidings, is in round numbers 180,000 

 miles, or about 45 per cent of the world's mileage. To locate 

 and construct these thousands of miles of road, much of it run- 

 ning through districts little or quite unknown when preliminary 

 surveys began, has involved a vast expenditure of money by 

 which geographic knowledge has been increased. It has been 

 estimated, perhaps it would be more exact to say guessed, that 

 the sums expended on these railroad surveys is enough to have 

 produced a topographic map of the entire country. The chief 

 geographic contribution from these surveys is a knowledge of 

 altitudes. Over all these railroads lines of level have been run, 

 and by collecting and platting those levels and adding to them 

 those obtained fr^m other sources, it has been possible for the 

 Geological Survey to produce a fairly approximate contour map 

 of the United States. 



The Mississippi river, with its tributaries in the great central 

 valley of the United States, drains an area of about 1.200,000 

 square miles, or about one-third of the United States. From the 

 sources of the Missouri to the passes at the mouth of the Mis- 

 sissippi in the Gulf of Mexico is 4,200 miles. These two great 

 rivers, with their affluents, afford thousands of miles of navi- 

 gable water through the great central valley. So important is 

 this artery of commerce that two distinct commis.sions, one for 

 the Mississippi and one for the Missouri, have existed for some 

 years for the purpose of surveying, mapping, studying, and im- 

 proving them. Detailed maps of the rivers and a fringe of topog- 

 raphy on either side have been made over a considerable part of 

 the navigable parts of these rivers, and the results are shown on 

 240 atlas sheets. Much precise leveling has also been carried on 

 in connection with these surve3^s. 



Independent of the Federal government, various states, to the 

 number of 20 or more, particularly those known to possess min- 



