128 The Ohio Journal of Science [Vol. XIX, No. 2, 



ENGULFED TREES SHOW THAT THE TUFF MUST HAVE ORIGINATED 

 AS A FLOW OF MUD. 



Finally, when our work carried us down the Valley toward 

 Naknek Lake, we found conditions, which, while rather adding 

 to the anomalies already puzzling us than explaining them, 

 yet gave such clear cut and positive evidence of the mode of 

 deposition of the tuff as to make its character certain. 



In the lower Valley, where the remains of the former forest 

 still persist to tell the tale, the "high water mark, " or as it had 

 better be called the "high mud mark," becomes even more con- 

 spicuous and significant than it is in the upper Valley. What- 

 ever our doubts may have been before, no matter how great 

 the difficulties of explanation that remained, one glance at the 

 remains of the forest embedded in this tuff was all that was 

 needed to convince everyone that we were dealing with a 

 gigantic mud flow. Right down to the edge of the erstwhile 

 rnud the trees stand undisturbed, but below that level they are 

 overriden, twisted and bent before it in such fashion as could 

 not have been done except by a moving liquid. The absolute 

 sharpness of this line separating the uninjured forest from that 

 covered by the moving mud is plainly shown on the photographs 

 reproduced on pages 126, 127, 128 and 136. 



At the bend in the Valley, where the forest begins, the mud 

 flow encountered a belt of irregular morainic hills among which 

 it pursued a most irregular course, overtopping some, leaving 

 others standing free above the surface, slopping over into 

 the ravines, and in every way showing that it was once highly 

 liquid. In this vicinity a strong stream, now furnishing the 

 greater part of the water of the Ukak River, was dammed by 

 the mud flow, forming a deep lake. Since the mud flow 

 hardened, the waters of this stream have cut down 20 or 30 feet 

 into this dam, but there still remains a lake a mile long and 

 half a mile wide. Beyond the bend in the Valley the mud flow 

 continued on for more than a mile, gradually thinning out until 

 for some distance back from the tip it is only 10 feet thick, in 

 striking contrast to its great thickness and massive character 

 further up the Valley. Everywhere the mud shows a surprising 

 capacity to adjust itself to the variations in the level of the 

 ground over which it flowed. At one place, near the middle of 

 the level flow, I noticed a tree or two sticking up through the 



