g8 



REPORT OF THE SECRETARY. 



is proposed to have this bulletin in rcadinesp for presentation before the 

 Berlin meeting of the Congres Geologique International during the 

 coming autumn. 



The taxonoraic scheme is essentially that published in the report for 

 1883, that is, as follows : 



Group. 



Ceuozoic . . 

 Mesozoic . . 



Paleozoic . 

 Azoic 



System. 



Quaternary 



Mioceuo 



Eocene (including Oligo- 



ceue). 



Cretaceous 



Jurasso-Triassic 



' Carboniferous (including 



Permian). 



Devon ian 



Silurian 



Cambrian 



Arch;ean 



Volcanic 



Sym- 

 bol. 



Q 

 M 



E 



K 

 T 

 P 



D 



S 



c 



A 



Color published. 



Gray 



Chrome yellow 

 Orange yellow. 



Dark green 



Olive green 



Blue 



Deep purple. . . 

 Light purple . . 

 Grayish purple 

 Brown 



Red 



Color proposed. 



Gray. 



Violet. 



Indigo. 



Blue. 



Green. 



Yellow. 



Orange. 



Red. 



Brown. 



Angular figures on 

 white ground. 



Round dots on neu- 

 tral ground. 



The sources of the information incorporated in the map are : first, 

 published maps, and second, manuscript maps prepared for the Survey 

 by diflerent ofiflcial and amateur geologists. As the colors have not 

 been carried beyond the boundaries of the original maps, this geologic 

 map may be regarded as an accurate representation of our present 

 knowledge of the distribution of American rock -groups. 



The map, together with the explanatory text, was prepared by Mr. 



W J McGee. 



Oeologij of the District of Columbia. 



The investigation of the superficial deposits, and the littoral and 

 fluviatile terraces of the District of Columbia and contiguous territory, 

 commenced in 1883 by Mr. W J McGee, were continued. A recon- 

 uoissance was extended over an area of 1,000 square miles having the 

 District of Columbia as its center. In addition, short journeys to the 

 northward and southward were made for the purpose of correlating the 

 deposits with those already known in other localities ; and, with the 

 same object in view, the literature of the Orange Sand and Stratified 

 Drift of the Gulf States, and the glacial " Quaternary," and accociated 

 deposits of the Atlantic States, were studied. In the prosecution of his 

 work Mr. McGee found it necessary to extend his observations into the 

 interior. The Potomac was followed as fiir as Cumberland, Maryland, 

 and the south branch of that river explored to its source in the elevated 

 tract near the center of the Virginias. Then crossing the main range 

 of the Alleghanies, Mr. McGee descended the Cheat, Monongahela, and 

 Ohio to Wheeling, West Virginia, re-examining the base-level, fluvia- 

 "tile, and lacustral terraces already noted by others on those rivers. 



