GEOPHYSICAL LABORATORY. 131 



This paper will be reviewed in its proper place (No. 480 seq.), but it is appro- 

 priate to review briefly the progress of the research as a whole. 



The two papers taken together have given us a comprehensive survey 

 of the gaseous emanations found in the Valley of Ten Thousand Smokes and 

 the scoriaceous material filling the valley through which they now emerge. 

 The emanations have been found to consist almost altogether of steam 

 (99.5 per cent or more), with small quantities of chemically active gases 

 (HCl, H2S, HF) and sulphur (chiefly in incrustations) near the probable 

 sources of the sand-flow. It has also been shown that the water supplying 

 the steam fumaroles in the Valley of Ten Thousand Smokes is supplied for the 

 most part from surface drainage, and that the activity of the fumaroles as 

 shown by the volume and temperature of the emanations is gradually dimin- 

 ishing. Nevertheless, most of the fumaroles are from deep-seated sources. 



Dr. Fenner has given attention particularly to the character of the sand- 

 flow itself and the manner of its deposition. He has shown conclusively that 

 the great deposit of scoria which now fills the valley can not have been 

 ejected from the Katmai crater. It is overlain by Katmai ash, and, more- 

 over, it is several miles away, with a region containing several glaciers inter- 

 vening, over which it could not have passed without destroying them and 

 leaving many unmistakable traces. The ash from the volcano shows strati- 

 fication, while the sand-flow, some hundreds of feet thick in places, shows 

 none. It was free from water and hot enough to reduce to charcoal the 

 trunks of trees embedded in it. 



The manner of distribution of the sand and scoria has also been studied 

 in detail and in certain of its phases has been found to compare closely with 

 the nu^es ardentes of Mont Pel6e, Martinique. It appears to have had many 

 sources through which it reached the surface and to have been highly charged 

 with hot, dry gases at the time of its emergence. There is nowhere evidence 

 that it was a "mud-flow." The manner of forward movement is that of an 

 avalanche of fine sand intimately mixed with dry gases, advancing with great 

 rapidity even over very low grades, as in the case of similar flows at Mar- 

 tinique. Occasional craters, some of considerable size, indicate that the hot 

 flow here and there encountered water, causing secondary explosions. 



Dr. Fenner's conclusion, offered for the moment as a working hypothesis 

 pending further investigations which are being conducted on the ground 

 during the present summer, is that a sill, which probably had its origin in 

 the same body of magma which found an outlet at Katmai crater, was driven 

 like a wedge under hydrostatic pressure between nearly horizontal strata of 

 shale and sandstone underlying the valley; that the upheaval produced by 

 the entrance of this sill served to shatter the valley floor throughout its whole 

 extent from the slopes of Mount Trident to the Ukak Outlet. Through 

 this shattered floor the valley drainage has had access to hot magma, and 

 in all probability the magma itself has broken through the floor at Novarupta 

 and perhaps elsewhere. The long life and high temperature of the fumaroles 

 indicate an intrusive mass of considerable volume. 



Through the courtesy of the U. S. Geological Survey, Dr. Fenner was 

 enabled to join one of their field parties in Alaska during the present summer, 

 and will no doubt discover further evidence regarding the sand-flow in the 

 Valley of Ten Thousand Smokes and the eruption of Mount Katmai itself, 

 which offers a most interesting and hitherto undiscussed problem. 



