10 SMITHSONIAN INSTITUTION 



which obviously must be visible from the observing station, a con- 

 siderable amount of exploratory work was necessary. As a result 

 of this, the known geographical range of fossil tracks in the Grand 

 Canyon was greatly extended and a considerable amount of new 

 material was secured for the National collections. Subsequent study 

 has shown some of the tracks to be undescribed, but the most note- 

 worthy specimen collected, from an exhibition viewpoint, is the large 

 slab from the Hermit formation shown in the accompanying illustra- 

 tion. This gives a vivid picture of the diversity of animal life that 

 once roamed over this ancient mud flat. 



An interesting development of these investigations was the dis- 

 covery by Mr. G. E. Sturdevant, Park Naturalist, of a track-bearing 

 horizon in the Bright Angel section of the Middle Cambrian. Thus 

 four distinct ichnite horizons are established in this one geological 

 section, distributed as follows : Coconino sandstone. 900 to 1,030 feet ; 

 Hermit, 1,350 to 1,400 feet; Supai, 1,760, to 1,800 feet ; and Tapeats, 

 3,600 to 3,800 feet below the top of the Canyon wall. 



On the south rim of the Grand Canyon, tracks have been found 

 on Grand View Trail on the east and Dripping Springs on the west, 

 these two localities being separated by a distance of 27 miles, and this 

 last exploration leads to the belief that tracks can be found in the 

 above mentioned horizons wherever the physical conditions will per- 

 mit search being made for them. In view of this last statement, it is 

 of interest to add that Mr. Sturdevant has recently discovered fossil 

 tracks in the Coconino and Supai formations on the north rim of the 

 canyon, some 14 miles distant in an air line from those found on the 

 south rim. 



