GEOGRAPHY OF NORTH AMERICA. 223 



triangles extending along the southern portion of the Appa- 

 lachian Mountains, and completing a continuous geodesic arc 

 from Passamaquoddy Bay to Central Georgia. This work, 

 with its five base-lines and numerous determinations of azi- 

 muth, latitude, and longitude, not only furnishes an exact 

 framework for the survey of the states through which it 

 passes, but is an important addition to our data for deter- 

 mining the figure and magnitude of the earth. 



Pursuing our review of the work around the shores of the 

 Gulf of Mexico, we find the survey completed from Cape 

 Florida to the Tortugas and Cape Sable. Some long reach- 

 es are yet to be mapped between the latter point and Cedar 

 Keys, on the w T est coast of Florida; but from this point to 

 the Mississippi delta the survey of the shores is unbroken. 

 West of this there are again several breaks until Ave reach 

 Galveston, whence the survey is again complete to Corpus 

 Christi. Offshore soundings are, however, still wanting 

 along a portion of the coasts just cited. Deep soundings 

 have been taken most successfully in the Gulf, developing 

 the form of this great basin, and, by the aid of temperatures 

 at all depths, its regimen and circulation. Work has been 

 in progress from Tampa Bay southward, in the vicinity of 

 Cedar Keys, on Barataria Bay, from Corpus Christi towards 

 the Rio Grande, and on the Mississippi River northward 

 from New Orleans. The latter work has a special value in 

 connection with the question of securing the banks from 

 overflow, and will be vigorously pressed a fresh point of 

 departure having recently been taken near Helena, Ark., 

 whence the survey will be carried to the head of ship navi- 

 gation, and will be met near Memphis by a transcontinental 

 chain of triangles, to which I shall presently refer. 



On the Pacific coast the survey has been in progress in 

 Southern California, especially on the Santa Barbara chan- 

 nels and adjacent islands a work rendered very difficult and 

 slow of progress by fogs and haze; also north of Point Con- 

 ception, above Cape Mendocino; on the coast of Oregon, on 

 the Columbia River, and in Puget Sound. Very notewor- 

 thy is the occupation of Mount Diablo and Mount Helena, 

 peaks of the Coast range, as the westernmost stations of the 

 great transcontinental chain, and the observation of angles 

 upon stations in the Sierra Nevada, forming some of the 



