"Boiler" and the "Black Growler" steam vents whose roar may be heard 1-2 mile, Yellowstone Park, U.S.A., The
One of the most popular regions of the Park is the Norris Geyser Basin, the highest geyser basin in the Park. Though the geysers of this basin are smaller than those farther south they are, in many ways, as interesting. The water of many of the geysers is impregnated with sulphur, giving them a milky, turbid appearance; unless they come in contact with iron when a black precipitate of iron sulphide is formed, making, at times, the water of some geysers as black as ink. The "Black Growler" is such a geyser. It does not throw out much water but keeps up a rumbling and spluttering, throwing out ...
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