316 
The American Geologist. 
May, 1895 
lines of railway which have been utilized in controlling the el- 
evation of the other roads. The lines of precise levels, there- 
fore, form the primary base lines, and the railway levels the 
secondary base lines. The latter form a complicated plexus 
or network of level lines upon which all mapping may be 
based. There are more than 6,500 miles of railroad in Mis- 
souri and more than 200 intersections, so that comparisons 
could be readily made at short intervals in order to bring out 
Sketch map 
SMOWlNa LOCATION OF I INES Of 
PRECISE LEVELIMa AND OF 
HAILWflY LINES WHOSE LEVELS 
ARf USE-D FOR PHlMARr 
CONTROL 
any discrepancies which existed. As has been stated, this has 
now been done. In some instances differences of nearl}'^ 50 
feet have been found in the previously determined elevations. 
With the completion of the revision of the altitudes of the 
state the foundation has been laid for detailed mapping both 
topographic and geologic for all Missouri. Any future 
changes in the recently determined figures which may be 
found necessary may be depended upon as being so small in 
value and as affecting the present results so slightly, that 
they may be practically neglected. In mapping which may 
be done before such minor corrections or adjustments are 
brought to light no essential changes in the cartography 
