98 HISTORICAL SKETCH

cuted by the United States Coast and Geodetic Survey for the control
of its coast work. For the eastern part of the state, including all the
Atlantic coastal plain, this triangulation is adequate for control. Its
points are sufficiently numerous and well distributed. It does not, how-
ever, extend west of the Blue Ridge at Harper's Ferry. Thence west-
ward the United States Geological Survey found it necessary to extend
triangulation for the control of its work, and owing to the difficult
character of the country, this extension of triangulation was quite
expensive, especially in the western counties comprised in the Alle-
ghany plateau.

From these primary triangulation points secondary points were
determined by triangulation with the plane-table, wherever it was
practicable to do so, but outside of the mountain and piedmont regions
the level character of the country precludes this method of making
locations.

The roads, railroads and other minor features were located by
traverses run by plane-table, connected at as frequent intervals as
possible with triangulation points for the elimination of cumulative
errors. Measurements of elevations for the location of contour lines
were carried on by vertical angles, measured upon the vertical circles
of theodolites, by spirit-level lines, and, for details, by aneroids.

The sketching of topography was carried on in the main in connec-
tion with the running of traverse lines.

The work of mapping the state was commenced at the western
extremity, in Garrett county, and was carried generally eastward.
The first work done was by a party in charge of Mr. S. H. Bodfish.
Subsequently, upon the failure of Mr. Bodfish's health, Mr. W. T.
Griswold took charge of the party and carried on the work during the
latter part of the season of 1883 and the seasons of 1884 and 1885.
In 1886 Mr. Merrill Hackett made a revision of the area surveyed by
Mr. Walling, adding cultural details. In 1887 the Baltimore, East
Washington and West Washington quadrangles were surveyed, the
former by Mr. S. H. Bodfish, the latter by Mr. D. J. Howell. In 1888
the Frederick quadrangle was surveyed by Mr. Hackett. In 1890 and
1891 the quadrangles on the west shore of Chesapeake Bay were