Contributions in geographical exploration . toascertain whether these (orres]jond with rock fissures or are ofa more superficial character. Where the vajior emerges fromsuch wide open faults in the tuff that covers the \alley. it isobvious that these might he merely the superficial avenues ofescape from the tuff, rather than the orifices of the true vents. 108 The Ohio Jounial of Science [Vol. XIX, No. 2, The linear arrangement in such cases may not be significant,therefore, but when there is no superficial break in the tuff cor-responding to the fine of smokes, it is difficult to explain thei
Contributions in geographical exploration . toascertain whether these (orres]jond with rock fissures or are ofa more superficial character. Where the vajior emerges fromsuch wide open faults in the tuff that covers the \alley. it isobvious that these might he merely the superficial avenues ofescape from the tuff, rather than the orifices of the true vents. 108 The Ohio Jounial of Science [Vol. XIX, No. 2, The linear arrangement in such cases may not be significant,therefore, but when there is no superficial break in the tuff cor-responding to the fine of smokes, it is difficult to explain theirarrangement in any other way than as being outlets of a funda-mental fissure in the bed rock. The writer, at least, can imagineno possible means by which such lines of smokes, often morethan a mile in length, could be explained on the surface waterhypothesis. But although the volume of the emanations, their chemicalcharacter, their temperatures and their arrangement all givevery clear and positive indications that they are true Photograph by R. F. Griggs LINES OF FUMAROLES ACROSS THE VALLEY. A portion of the valley floor where the linear arrangement of the fumaroles is very conspicuous, indicating that they spring from fissures traversing its floor or encircling its edges. we were very unwilling to consider the matter settled untilwe could find ocular evidence of their actual emergence fromorifices in the bed rock underlying the Valley. But this proved to be a matter of considerable difficulty,for the Valley is everywhere filled with a very thick depositof the peculiar tuff which is discussed in the succeeding was good reason to believe, as will be seen, that the smokesdid not originate in the tuff itself, but it so plasters up theValley that it is difficult to ascertain the character of the groundfrom which they do emerge. As we prosecuted the exploration,therefore, we were constantly on the watch for evidence whichwould throw Hght on the source of the
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