Dec, 1918] Are the Ten Thousand Smokes Real Volcanoes? Ill 



ing the character of such deposits. We were not wiUing to 

 adopt so important a hypothesis unless we could find conclusive 

 proof of its correctness. We were the more cautious in this matter 

 because the underlying rock was not lava nor igneous rock of 

 any kind, but sedimentary sandstone strata, as could be clearly 

 seen in the bed of the adjacent stream. 



Early in the exploration we observed the numerous fumaroles 

 that come out of the upper slopes of Falling Mountain (see 

 page 112). But since these occur in an ancient volcanic mass it 

 was not certain that they could rightly be considered similar 

 to the vents of the Valley. 



Our uncertainties continued, therefore, until finally on the 

 Broken Mountains, which are surrounded on all sides by the 

 active vents of the Valley, we came upon several groups of 

 small fumaroles which set at rest all possible doubts. The}'- 

 were located on almost precipitous slopes, (see page 105), from 

 which all loose ejecta had slumped away, leaving the bed rock 

 exposed to view. Here there could be absolutely no question, 

 for the little fumaroles were coming directly from the sandstone 

 strata, emerging from the crevices in the rocks which lay evenly 

 bedded in undisturbed layers as originally deposited. The 

 little crevices through which they found their way out had no 

 doubt been broken open by the general disturbance, which so 

 thoroughly broke up these mountains as to have suggested their 

 name. But at these particular places the eruption had shattered 

 the rock so little as not to disturb the position or arrangement 

 of the original strata. 



It is, of course, quite unnecessary to add that such fumaroles 

 could not originate in the sandstone, but must have come from 

 some mass of intruded magma beneath the surface. The very 

 smallness of these little fumaroles made them all the more 

 significant, for if these little wisps of steam were proven to come 

 out from beneath the bed rock, the great columns of vapor in 

 the adjacent Valley must as certainly draw their energy from 

 the interior of the earth. 



MAGMA REACHED SURFACE IN NOVARUPTA VOLCANO. 



The magma that must thus underlie the w^hole of the Valley 

 comes to the surface at one point — the crater of Novarupta 

 (see pages 112, 113 and 114). This vent, which is in every way 

 a typical volcano, has burst through the floor of the Valley like 



