Dec., 1918] The Great Hot Mud Flow 119 



I would further add that I am not committed to any theory 

 of the origin of this curious terrane, but will be glad to accept 

 any other interpretation that can be suggested, provided only 

 that it is consistent with the facts as found in the field. Certainly 

 any suggestion that would relieve us of the necessity of postu- 

 lating an entirely new type of volcanic action will be most 

 welcome. 



VALLEY OF TEN THOUSAND SMOKES FILLED WITH A GREAT 

 DEPOSIT OF TUFF. 



Surrounded as it is by high and nigged mountains, the most 

 striking feature of the conformation of the Valley of Ten 

 Thousand Smokes is the flatness of its floor. One could ride 

 a bicycle for miles along its smooth surface, and there are many 

 places between the lines of activity that would be ideal landing 

 fields for airplanes. (See map, page 138). 



Where the drainage gullies have gashed this surface, its 

 flatness may be seen to be due to the smooth top of the terra 

 cotta tuff already mentioned. The traveller peers into these 

 canyons in the hope of finding some clue to the thickness of 

 this massive tuff, but in this he is disappointed. In such places 

 one finds cuts of 40, 60, or even 100 feet down into its mass, 

 but none of these, in the upper portion of the valley, reach its 

 base and reveal the character of the formation beneath. This 

 is not only very puzzling, but very impressive as well, for when 

 one finds that it is more than 50 feet thick over wide areas, it 

 becomes evident that the volume of the formation is enormous. 

 Our inability to find any section through it was rendered the 

 more significant by reason of the fact that almost all of the 

 trenches in it are located not in the middle of the Valley, where 

 it might be supposed to be thickest, but along the edges where a 

 minimum thickness would be expected. (See page 118). 



The enormous volume of this mass was further emphasized 

 as we extended our exploration through the Valley,^for then 

 it became evident that the area covered by it was much greater 

 than had appeared from the head of the Valley. First we found 

 the branch valley heading in the Broken Mountains covered 

 with it. Then we saw the great valley between the Broken 

 Mountains and Knife Peak all filled in the same way, clear 

 back to Novarupta Volcano, forming with the main valley a 

 complete circuit around the Broken Mountains. Finally, 



