PLAN OF THE MAP. 



The scales which have finally been adopted for the publication of the 

 map are 1:62500 or very nearly 1 mile to an inch, and 1:125000, or very 

 nearly 2 miles to an inch. 



When this work was commenced in 1882, three different scales were 

 used for different parts of the country, depending- upon the degree of com' 

 plexity of the topography and the geological phenomena, upon the density 

 of population and the importance of the region from an industrial point of 

 view. These scales were 1:62500, 1:125000, and 1:250000. The maps as 

 fast as produced have found extended use, not only among geologists, but 

 in all sorts of industrial enterprises with which the surface of the ground is 

 concerned, and have already become well nigh indispensable in the pro- 

 jection of railroads, water works, drainage works, systems of irrigation, and 

 other similar industrial enterprises. Their extended use has developed a 

 requirement for better maps ; i. e., maps upon a larger scale and in greater 

 detail. At one stage of its development this requirement was met by dis- 

 continuing all mapping upon the scale 1:250000, which it was recognized at 

 that time was inadequate to the requirements. Since then the standard of 

 the requirements has continued to rise and, consequently, the plan of the 

 map has been enlarged by the extension of the areas mapped upon the scale 

 of 1:62500, and a corresponding reduction of the areas to be mapped upon 

 the scale of 1:125000. Meantime, however, large areas have been mapped 

 upon the discarded scale, and the maps have been published and widely 

 distributed. Such areas will be remapped for the larger scales only as 

 special needs may arise. 



The considerations which have determined the selection of the above 

 scales are as follows: They are believed to be sufficiently large to represent 

 with faithfulness all the details required to picture the country and show the 

 proper relations of its features, and to make the map of the greatest pos- 

 sible service for industrial and scientific uses consistent with other require- 

 ments to be mentioned hereafter. These scales are sufficiently large to 

 present the details of nearly all geological phenomena. The map represents 

 the country in sufficient detail to admit of the selection upon it of general 

 routes for railroads and other public works and to show the location of 



