It need hardly be said that hydrographic surveys have been of great service to compilers of maps.
C. Fremont and Howard Stansbury (1806-1863) furnished a general knowledge of the hydrographic features and geological lacustrine history of the Great Basin, and this knowledge was rounded out by the field work of the U.S. Geological Survey from 1879 to 1883, under the direction of Grove Karl Gilbert.
Sailing directions for Lake Michigan, Green Bay, and the Strait of Mackinac, U.S. Navy Hydrographic office publication No.
South of this enclosed depression is another great hydrographic barrier which parts it from the low plains of the Amur, of China, Siam and India, bordered by the shallows of the Yellow Sea and the shoals which enclose the islands of Japan and Formosa, all of them once an integral part of the continent.
The variations themselves are detected by the method of seasonally repeated hydrographic soundings.