Prof. B. 8. Lijman — Contour Lines on Geological Maps. 133 



for the exploitation of the deepest part of the basins ; and more 

 particularly to establish the best elevation at which to drive gang- 

 ways to command the greatest area of coal with the least expendi- 

 ture, for the driving of permanent travelling ways and the lifting of 

 the coal and pumping of the mine water. 



"/. It is a well-known fact to the practical mining geologist that, 

 .... when the axial plane is inclined, the axis in the outcropping 

 strata may be many feet to one side or the other of a vertical plane 

 passing through the axis in the coal bed. 



" (/. It is apparent that a vertical section of the contoured coal bed 

 may be constructed directly from the curves, running across the 

 basin in any direction. The position on the section plane of the over- 

 lying and underlying strata may be located from columnar sections. 



" /*. One of the most important applications of this method of 

 construction is the estimation of the absolute areas of the coal beds 

 under any given tract, and consequently the coal contained. It is 

 readily perceived that consequently, when the contoured surface of 

 the bed is developed or ironed out into a horizontal plane, allowance 

 will have been made for every degree of dip which the bed possesses 

 in its true position, and the real area of the bed on the flat will be 

 shown." 



On the Mine Sheets so far published the underground workings 

 of several coal beds are given in different colours, besides the con- 

 tours of the floor of the principal bed, and " the confusion and un- 

 sightliness of so many lines upon a map," complained of by your 

 critic, is not enhanced by the addition of the contours of the surface 

 of the ground, for (p. 15) " the topographical maps which have 

 come into the possession of the Survey have not been found suf- 

 ficiently accurate to make it possible to combine them in this way 

 with the mine sheets constructed by the Survey corps, without com- 

 pletely revising them on the ground. As the restricted means of 

 the Survey have prevented this revision, it was decided to publish, 

 these maps separately, and on one-half the scale of the Mine Sheets, 

 in order to reduce the cost of publication. The difference of scales 

 makes a comparison of the two sets of sheets inconvenient. 



" Before the completion of the Geological Survey of the Anthra- 

 cite Fields, it is hoped that surface contour curve maps may be 



constructed by the corps of the following areas 



In some of these areas the contours of the surface can no doubt be 

 placed to advantage on the mine sheets without overloading the map 

 to such an extent as to produce confusion." 



Of course " confusion and unsightliness" depends much upon the 

 experience of the reader, and a mere contour map of the surface will 

 have that character to anybody unaccustomed to contours. While real 

 confusion is certainly to be avoided, a good deal of what seems at 

 first unsightliness may be pardoned if compensated by usefulness 

 and convenience in use. Indeed, thei'e is much truth in the common 

 saying that " handsome is that handsome does " ; for our ideas of 

 beauty are at the very bottom altogether based upon fitness for our 

 needs. It seems at least possible that the most crowded mine sheets 



