HYDROGRAPHY IN THE UNITED STATES 
149 
and to connect these intimately with the mapping of the topog- 
rapher and the studies of the geologist. 
Passing from the many small streams of the country to the 
larger, navigable rivers, the work of the Engineer Coi’i^s of the 
Arm}'’ is reached. As far as this relates to hydrography, the sur- 
veys of the Engineer Corps consist of examinations of particular 
points with the object of obtaining information preliminary to 
construction for the benefit of navigation. A considerable num- 
ber of river gauges have been maintained and readings continued 
in order to ascertain the periods of low and high water and to 
obtain other data essential to correct plans. A few measure- 
ments of volume havebeen made upon some of the larger streams. 
^^'ith the work of the Engineer Corps can l)e placed that of the 
INIississippi and Missouri River Commissions, these organizations 
having conducted series of observations throwing light upon the 
behavior of these great rivers. Nearly related to this has been 
the work of the Lake Survey, conducted by army engineers, who 
have ju’epared detailed maps of the shores, showing the harbors, 
passages, and depths of water at all the shallow places. 
At the head of tide water begins the work of the United States 
Coast and Geodetic Survey. This, the oldest of the surveying 
organizations of the Government, maps the navigable tidal waters 
of the United States from the remotest waters to tlie shore line 
and from the shore lipe outward to the oceanic abyss, studying 
the currents and fluctuations of water surface and map])ing in 
great detail the harbors, shoals, cliannels, and all other features 
■of importance to mariners. The investigations of this Survey 
have Ijeen conducted with the utmost accuracy, and its charts 
and ])ublications relating to hydrograi)hy have reached tlie 
liighcst ])oint of scientific attainment. With the work of the 
Coast Survey may be considered that of tlie Light-house Board, 
also a bureau of the Treasury Department, which in a relatively 
more limited and less detailed way has made hydrogra])hic sur- 
veys for the ])urp()se of erecting danger signals or light-houses, 
and has thus contributed somewhat to the knowledge of the 
navigable waters. 
Extending beyond the bounds of the Uniteil States, our knowl- 
edge of the hydrography of the great s(‘as is being added to by 
the Hydrographic OHice ol' the Navy, which bi-ings together and 
]»ublishes maps, charts, and everything of interest to mariners 
relating to foreign lands, and covering with jierhaps less minute- 
ness the shores of other countries in a iminner similar to that 
