258 National Geographic Magazine. 



before the American Institute of Mining Engineers in 1887; 

 The method was published in 1838. Upon a contoured map as a 

 basis cross-section lines are drawn at small and regular intervals, 

 and, if the topography be intricate, corresponding lines at right 

 angles. The sections thus secured are transferred to thin strips of 

 some suitable material, such as cardboard or metal, and cut down 

 to the surface line, — the strips themselves thus forming the cross- 

 sections. These cross-sections are mounted upon a suitable base- 

 board, and the cavities or boxes are then filled up with some 

 easily carved material, such as plaster or wax. The top is then 

 carved down to the form of the country or district, — the neces- 

 sary guidance being obtained by the upper edges of the strips 

 that form the cross-sections. It will be readily seen that this 

 method is a very crude and laborious one. It necessitates in the 

 first place a good contoured map upon which to draw the sections, 

 but sacrifices much of the advantage thus gained because only a 

 number of points on each contour line are used, instead of the 

 entire line. It is no better, although actually more laborious, 

 than the later method of driving contour pins (whose height 

 above a base-board may be accurately measured,) along the 

 contour lines, and then filling in. A slight modification of the 

 latter method can be used to advantage when no contoured map 

 is available, and when the points whose elevation is known are 

 not numerous enough to permit the construction of one. In this 

 case the only control that can be secured is \)j means of a num- 

 ber of pins driven into the base-board at those points whose 

 elevation is known. The remainder of the map is then sketched 

 in. This method is perhaps as satisfactory as any, when the 

 material upon the map is scanty. Another method, however, 

 growing out of the same scantiness of material, is in some cases 

 to be preferred, especially for large models. The map is enlarged 

 to the required size, and a ti'acing of it is mounted upon a frame. 

 Another deep frame, just large enough to contain the mounted 

 tracing, is made, and laid upon a suitable base-board upon which a 

 copy of the map has been mounted. Upon this base-board the 

 model is then commenced, in clay or wax. The low areas are 

 modeled first, — horizontal control being obtained by pricking 

 through the mo.unted tracing of the map with a needle point, 

 and vertical control by measuring down from a straight edge 

 sliding on the top of the deep frame. This system is rather 

 crude, and onl}' useful where the material upon the map is very 

 scanty, but it gives excellent control. 



