88 



REPORT OF THE SECRETARY. 



is proposed to have this biilletin in readiness' for i)resentation before the 

 Berlin meeting of the Congres Geotogique International dnring the 

 coming antamu. 



The taxouomic scheme is essentially that published in the report for 

 1883, that is, as follows : 



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

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

 by different ofiicial 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 prej^ared by Mr. 



W J McGee. 



Geology 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- 

 noissance 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 

 w^ork Mr. McGee found it necessary to extend his observations into the 

 interior. The Potomac was fi)llowed as far 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 Alleghauies, Mr. McGee descended the Cheat, Mouongahela, and 

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

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



