REPORT OF THE SECRETARY. 



77 



of the distribution of American rocks, is now being colored geologically. 

 The base is that employed in the atlas accompanying the final reports 

 of the Tenth Census, which corresponds in size to the double atlas- 

 sheets of the survey. Since the minor divisions of the geologic column 

 cannot be indicated upon so small a scale, and since, moveover, our 

 information respecting the rocks of various regions is insufficient for 

 nice discriminations, only the general divisions will be represented on 

 this map. These divisions are indicated by symbols and colors. The 

 following is the scheme adopted : 



To an extent, the map is an experimental one ; and the method of 

 geologic cartography and the system of geologic classification to be 

 ultimately adopted by the Survey are being developed as the map pro- 

 gresses. At the same time, since the sources of information drawn upon 

 in its preparation embrace not only the latest publications (both official 

 and unofficial), but also much unpublished material in the hands of 

 different attaches of this Survey, of several State geologists, and of 

 various amateur geologists, the map may properly be regarded, when 

 completed, as the most satisfactory representation of American rocks 

 extant. It is essentially complete in manuscript, and will probably be 

 published within a few months. It is the present intention, indeed, to 

 lay it before the Congres Geologique Internationale at the approaching 

 Berlin meeting, as an illustration of the system of cartography and 

 classification finally adopted by the Survey. 



The work is in the hands of Mr. W J McGee, who has had for a 

 time the collaboration of Prof. C. H. Hitchcock. 



Paleontologic Work. 



WorTi of Prof . 0. C. Marsh. — The search for extinct vertebrate re- 

 mains and their study has been assigned to Prof. O. C. Marsh. During 

 the season of 1883 he has had field parties at work in Colorado, Wyo- 

 ming, and Oregon. Professor Marsh himself spent the month of August 



