academy op sciences] CHIEF GEOLOGIST, NATIONAL SURVEY 171 



The standardization of the survey maps began in 1881 with an announcement in Powell's 

 first report — the second of the series — regarding a scheme of geological colors to which reference 

 has already been made. A more important step was made in 1887 when Gilbert, acting for 

 Powell, sent a letter to 12 leading geologists, inviting them to a conference on map problems. 

 The letter included the following significant statement concerning map sheets: 



As our plan involves the preparation, sooner or later, of about 6,000 of these sheets, the method of publica- 

 tion is worthy of the most careful and thoro investigation we can give it. 



Following the conference Gilbert issued an account of the plan adopted. After declaring 

 the survey areal unit to be an atlas sheet, not a State, he went on : 



We assign an atlas sheet to a field geologist, who is not a paleontologist, and instruct him to map the forma- 

 tions that he finds without regard to correlation, treating his area practically as though it was the first area 

 ever mapped. For his purposes, a "formation" is a stratigraphic unit of such order as his map scale permits 

 him to plat. He collects fossils but does not study problems of correlation. . . . Formation names are local and 

 so are formations. Some will appear on but one atlas sheet, and we propose to carry none farther than we can 

 find good physical basis. Detailed correlation is a work for the paleontologist, and for the broad view. It is 

 to be prosecuted in the interest of general geologic history, and it has slight bearing on problems of stratigraphy 

 and economic geology. It can be done at any time, and can be done over as often as the progress of the science 

 requires. But the map, if faithfully presenting the physical or stratigraphic phenomena, is of permanent value, 

 and needs no amendment to bring it into conformity with new views. This plan of ours is the outcome of not 

 a little study and experiment, and it appears to us that if we attempted the alternative plan of correlating in 

 detail before we decided what to map and what names to use, we should never accomplish anything in areal 

 geology. 



Another step was taken at the end of 1888, when a circular letter, this time signed by Powell, 

 was sent out to a larger number of geologists, asking for comments and suggestions on the gen- 

 eral questions involved in map publication; and the replies were considered in January, 1889, 

 by a committee of 18 members under the chairmanship of the director. One of Gilbert's letters 

 summarizes the action then taken more pointedly than was done in the formal report upon it: 



The past week has been chiefly devoted to a conference on the plan of publishing our geologic maps. Powell 

 called here a number of his assistants living in other cities, and these, with the Washington chiefs of divisions, 

 made a roomful, who spent four whole days discussing the various scientific and practical questions involved. 

 Everybody had ideas and opinions and each recognized great gain from the interchange. Most of the questions 

 were satisfactorily settled, and the principal one left unsettled was one requiring experimentation. Powell 

 shines as moderator of such an assembly, for he has rare power of keeping the main point in focus. 



The results thus reached were published in the tenth annual report of the survey. It 

 may be questioned whether any other national survey ever began the publication of its maps 

 with so carefully considered a plan touching every detail of terminology and coloration. As 

 examples of the rulings then established the following extracts are presented: 



A formation should be recognized and called by the same name as far as it can be traced and identified by 

 means of its lithologic characters, aided by its stratigraphic association and its contained fossils. ... In 

 the application of formation names, the laws of priority and prescription shall be observed. . . . Maps are 

 designed primarily for the use of the citizens of the United States, whether geologists or laymen. . . . The 

 unit of publication shall be an atlas sheet with legend on margin, accompanied by a full sheet of letter press de- 

 scription (so prepared as to be intelligible to men who are not trained geologists), and where necessary, by a 

 sheet of sections exhibiting the structure of the area. 



The nongeological nationals of the United States ought to have been as much flattered by 

 the consideration given to their needs in this plan as they must have been dismayed on seeing 

 the measure of intelligence expected of them when the maps were issued. 



One of the novelties of the plan was the adoption of blue instead of gray for the coloring 

 of Carboniferous formations; but it was properly pointed out that, while gray might be appro- 

 priate if the Carboniferous were always carboniferous, blue was as appropriate as gray for a 

 formation that, in the United States at least, was represented by a marine limestone over a 

 larger area than that in which it included coal beds. But this was a subordinate matter; the 

 marvel of the color scheme adopted was the ingenious manner in which it was made available 

 for several thousand map sheets and for several hundred formations. It was explained that if 

 each local formation had a special combination of color and pattern, the scheme would become 

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