207] W. B. Clark 9 



In 1778 Charpentier 7 published a book on the mineralogy 

 of Saxony accompanied by a so-called petrographic map on 

 which red is used for granite, purple for gneiss, pink for 

 schists, blue for limestones, gray for gypsum, yellow for sand- 

 stone, drab for river sand, and green for clay and loam. 



Palassou in 1781 8 published an essay on the Mineralogy of 

 the Pyrenees in which the routes in the south of France are 

 colored according to the rocks they cross : green for granite, 

 yellow for schists, and red for limestone, while sands, sand- 

 stones, and clays are indicated by signs, as are also extinct 

 volcanoes. 



Much the most important of these early colored geological 

 maps were those of William Smith, who prepared fifteen 

 county geological maps of England between 1794 and 1821. 

 These and his general geological map of England published 

 in 1815 mark the beginning of modern geological cartography. 

 Many refinements have been introduced in subsequent years 

 and an attempt more or less successful has been made to 

 secure cooperation on the part of geologists the world over in 

 the use of the same colors for rocks of the same age and char- 

 acter. At first all maps were colored by hand, but in recent 

 years lithographic processes have been introduced, although 

 the Geological Survey of Great Britain continued to color its 

 geological maps by hand until a few years ago. The Mary- 

 land Survey has made only colored lithographic geological 

 maps. 



In addition to the strictly geological work carried on by the 

 instructors and students of the Geological Department to 

 which I shall again presently refer, the Survey has secured 

 the cooperation of the staffs of several Federal and State 

 Bureaus (1) in the making of the base topographic maps, 

 necessary not only for the geological but other kinds of sur- 

 veys; (2) in the classification and platting of the agricultural 

 soils which are the disintegrated surface portions of the geo- 



Mineralogische Geog. d. Chursachsische Lande, 1778. 

 Essai sur la Mineralogie des Monts Pyrenees, Paris, 1781. 



