96 Trans. Acad. Sci. of St. Louis. 
ever, twice as great, the contour interval is 20 ft. instead of 
50 ft., the township and section lines are added and the dis- 
tribution of the formations and other geological facts are 
shown.* The adoption of the larger scale permits the repre- 
sentation of much valuable detail which is omitted from the 
U.S. Geological Survey sheets and the methods used insure 
much greater accuracy in the determination of both horizontal 
position and altitude. 
The methods by which these maps are constructed are some- 
what different from those used by the U. S. Geological Survey. . 
They are the outgrowth of work prosecuted under the writer’s 
direction during the past four years; they are the most satis- 
factory, to his knowledge, for accomplishing all the ends in 
view, both with regard to cost as well as quality of product. 
The geographic co-ordinates of the sheet have first to be 
determined. For this purpose the results of the triangulation 
of the U. S. Coast and Geodetic Survey, and of the Missis- 
sippi and Missouri River Commissions are used where appli- 
cable ; elsewhere astronomical determinations have been made. 
These results furnished the primary horizontal control, and 
subject to such control, the township and range lines are 
located on the sheet. Within each cadastral township, so 
outlined, the section lines were located from the Land Office 
sheets, discrepancies within such townships being distributed. 
The railway lines were plotted from the maps of the respect- 
ive roads and these, together with the section and other land 
division lines, served as lines of horizontal control. The 
drainage has been plotted, in part, from the Land Office sheets, 
at least the points of intersection of streams and section lines 
have been generally obtained in this way. Such locations are, 
however, checked by frequent intersections with the meander 
lines of the topographic work. Vertical control for contour- 
ing is obtained primarily from the precise leveling of the 
Coast and Geodetic Survey and of the River Commissions and, 
secondarily, from the profiles of the various railways. In 
addition to these, lines of level are run by the Geological 
Survey through each township, which furnish frequent bench 
marks and, in addition, fix with exactness the relative eleva- 
* A section sheet accompanies this map, as issued by the Geological 
Survey, showing the structure of the area and details of the stratigraphy. 
