THE NATIONAL GEOGRAPHIC MAGAZINE 



137 



The marginal fissures usually stand 

 open, like great cracks in the surface, 

 into which one might fall unless careful. 

 Sometimes the fissures were formed 

 merely by the cracking open of the 

 ground, but often they are lines of fault- 

 ing, one side standing higher than the 

 other. They are often steaming hot for 

 long distances without a break, and at in- 

 tervals contain vents from which issue 

 some of the biggest smokes in the valley. 



While the smoke from the craters 

 comes out quietly, in vast, rolling clouds, 

 that from the fissures often is emitted 

 under considerable pressure, roaring and 

 hissing. If one tosses pebbles into the 

 mouths of these vents they are so buoyed 

 up by the rising gases that they are either 

 immediately spewed out again or they sink 

 slowly down through the rising steam like 

 feathers settling to earth. Such vents are 

 the hottest places in the valley ; the gases 

 from them do not condense for several 

 yards beyond the orifice (see page 127). 

 They furnished some of the most satis- 

 factory places for the collection of gases 

 for analysis, because of the ease with 

 which the collector could assure himself 

 that his sample was free from contamina- 

 tion with the atmosphere. 



The fissures of the central valley floor, 

 unlike those along the margin, do not 

 stand open, but are often recognizable 

 only by the lines of incrustations de- 

 posited along them. Although they also 

 contain some of the largest vents, the gas 

 from many of them is not visible on a 

 bright, hot day, and only during wet 

 weather does one realize, by the long 

 lines of little smokes he sees stretching 

 across the valley in every direction, how 

 much gas such fissures are continually 

 pouring out into the air. 



Naturally we were anxious to find out 

 how deep some of these fissure were, but 

 we could not gratify our curiosity. To 

 sound some of the less active vents with 

 a stone tied to a rope was easy, but this 

 line was only 100 feet long and was too 

 short to reach the bottom of those we 

 tried. 



The greater part of the gas given 

 off is undoubtedly steam, but even the 

 smaller vents contain many substances, 

 in addition, which must have originated 



deep down in the earth. In many of the 

 larger and hotter vents the proportion 

 of other gases increases so greatly that 

 the emanation is changed in character and 

 does not look like steam, but takes on a 

 bluish cast like the smoke from the com- 

 bustion of a fire. In a few cases this 

 blueness is so pronounced as to be no- 

 ticeable at a distance of several miles. 



The principal cause of this blue smoke 

 appears to be sulphur dioxide, the same 

 gas that is given off by burning sulphur. 

 Other factors probably cooperate in pro- 

 ducing this appearance, but in what de- 

 gree they are responsible cannot be de- 

 termined until the chemical analyses are 

 completed. 



A BEWILDERING COMPLEX OF ODORS 



The many substances rising through 

 these vents result in an extremely curious 

 combination of odors, which Dr. Shipley, 

 with the trained nose of a chemist, thus 

 describes : 



"As we entered the valley along a deep, 

 dry, watercourse, we observed, from time 

 to time, a peculiar, indefinable, and not 

 unpleasant odor. Passing close to the 

 active vents, the odor of hydrochloric 

 acid and hydrogen sulphide could be de- 

 tected easily. From certain of the active 

 areas a disagreeable smell, unlike any 

 odor that we had ever encountered, arose. 

 It was somewhat suggestive of a pig- 

 sty, a horse-stable, and sewer gas, yet we 

 could not relate it definitely to any previ- 

 ously observed smell. 



"Whatever the gases are, that rise from 

 the vents in the floor of this wonderful 

 valley, collectively they offer a consider- 

 able task to the olfactory organs in differ- 

 entiating the known from the unknown. 

 At a distance of 20 miles from the valley, 

 one was certain one moment that the gas 

 was sulphur dioxide which the wind bore 

 to him, the next moment it was hydrogen 

 sulphide, and the next, both or neither. 

 This same elusive uncertainty clung 

 throughout the whole period of our stay 

 in the valley. It was only in the vicinity 

 of a vent that the individual gases could 

 be identified with certainty by the sense 

 of smell.' , 



All of the vents, even the smallest, 

 whose fumes are too slight to be visible, 



