Davis — Notes on the Colorado Canyon District. 259 



seems explicable as a result of underground drainage. Sink 

 holes of various sizes are found on the Kaibab uplands, and 

 Dutton reports that large springs issue from the walls of the 

 Kaibab canyon (1. c, 138, 196). 



It was impressed upon me throughout our excursion over 

 the plateaus that a multitude of problems connected with the 

 history of the canyon district await solution. The earlier 

 explorers gathered a great harvest there, and presented their 

 results so vividly that newcomers may enter the region as if 

 already acquainted with it. But the gleanings that the earlier 

 explorers left are abundant ; local structural studies as well as 

 such considerations as are involved in dates of faulting, origin 

 of stream courses, cycles of erosion and past climatic condi- 

 tions, offer plentiful material to investigators for years to come. 

 Harvard University, July, 1900. 



