Topographic Models. 255 



of hachures may be roughly characterized as a graphic system. 

 with a conventional element, and the contour method as a con- 

 ventional system with a graphic element, — for if the contour 

 interval is small enough a sort of shading is produced which 

 helps considerably the idea of relief. 



In addition to these two great systems, with which everyone is 

 more or less familiar, there is another method of representing a 

 country or district, — a method that succeeds where others fail, 

 and which although by no means new, has not received the atten- 

 tion it deserves: this is the representation of a country by a 

 model in relief. Certain striking advantages of models over 

 maps of all kinds are, indeed, so apparent that one almost loses 

 sight of such slight disadvantages as can, of course, be urged 

 against them. In the graphic representation of the surface they 

 are far superior to the hachured map, and they have the further 

 advantage of expressing the relative relief, which the hachured 

 map fails to do, except in a very general way. They have also 

 the advantage of showing actual shadows, exactly as they would 

 be seen in a bird's-eye view of the district, instead of more or 

 less conventional ones, and are, consequently, more easily com- 

 prehended by the layman, without becoming any less valuable to 

 the skilled topographer. In short, they combine all the graphic 

 features of a hachured map with all the advantages of the best 

 class of contoured jnaps, and in addition they show more of the 

 surface detail, upon which so much of the character of the 

 country depends and which is very inadequately expressed by 

 hachures and almost completely ignored in a contoured map of 

 large interval. The contours themselves can be made to appear 

 upon the model very easily and without interfering with other 

 features. 



The uses of models are many and various. Within the past 

 few years their usefulness has been much extended, and, now 

 that they are becoming better known, will probably receive a 

 still further extension. To the geologist they are often of great 

 value in working out the structure of complicated districts, for 

 the reason that so many important structural relations can be 

 presented to the eye at a single glance. Similarly, for the 

 graphic presentation of results there is no better method, as the 

 topography, the surface geology, and any number of sections 

 can be shown together and seen in their proper relationship. To 

 the engineer an accurate model is often of the greatest assistance 



