A Hypsometric Map of 3Iissouri. — Keyes. 315 
sidered railroad levels are depended upon almost entirely to 
give starting points for subsequent determination of altitudes 
by barometrical means. Unless carefully checked, however, 
railroad levels are sufficiently inaccurate to render untrust- 
worthy all attempts to establish a reliable datum for detailed 
mapping and to give rise to very erroneous results in the 
calculations involving the elevations of particular places. 
Thus, figures from this source which are liable to vary several 
feet in either direction usually interfere seriously with accu- 
rate work and in many cases practically make negatory the 
results sought, as may be subsequently shown by lines of level 
more carefully run. 
This was the condition of things which confronted the Mis- 
souri Geological Survey at the beginning of its work of de- 
tailed topographic mapping. To relieve this uncertainty in 
regard to the starting points, the profiles of the railroads 
traversing the state and the lists of elevations of all stations 
on them were collected. Within the past year the recalcula- 
tion of all points, their adjustment to more accurate datum 
lines, and their reduction to mean tide level has been finished. 
An essential aid to this work has been the various lines of 
precise levels which have been run under Federal auspices. 
Missouri has been especially favored in this respect. The 
Mississippi River Commission has established a line along the 
entire eastern border of the state. This is part of the series 
started from Biloxi on the Gulf of Mexico and carried up the 
Mississippi river. The Missouri River Commission has taken 
up the work from the mouth of the Missouri starting with a 
bench mark of the organization just mentioned and has car- 
ried it across the state to Kansas City and from thence north- 
ward along the western boundary, to beyond the Iowa line. 
The U. S. Coast and Geodetic Survey has also run a line of 
levels, as a part of its transcontinental work, along the Mis- 
souri Pacific railway from St. Louis to Kansas City, and also 
from the latter point southward near the western boundary 
into Arkansas. Where the lines of railway intersect those of 
the precise levels there is afforded an accurate basis of the cor- 
recting of any errors which may exist in the former. In the 
accompanying sketch map of Missouri there are shown the 
lines of precise levels which cross the state and the principal 
