28 



SMITHSONIAN INSTITUTION 



Fig. 23. — Another view of the large algal masses found in the shales of the 

 Nankoweap Valley. The pictures represent masses washed into the gullies ; 

 it is not possible to photograph entire colonies in position. (Photograph by 

 Resser.) 





Fig. 24. — A. A. Stoyanow and Robert E. S. TTeineman of the Arizona State 

 Geological Survey, standing by a cholla or jumping cactus, so called because 

 the smaller branches cling so easily and persistently to shoes and clothing. 

 In fact the heat or moisture of one's hand held close causes the branches to 

 turn toward it. (Photograph by Resser.) 



