HEAT. 



305 



Thermal Waters, Geysers. 



278. 



Geyserite Terraces, from the "Pink 

 Terrace" of New Zealand. 



The subject of thermal waters constitutes an important part of Chemical 

 Geology, and is here only briefly treated. Hot springs are (1) common in 

 volcanic regions, and (2) occur also along the courses of non-volcanic erup- 

 tions. They are occasionally met with, away from all igneous eruptions, (3) 

 on the lines of faults or the axes of flexures, and sometimes (4) where there 

 are none of these conditions. The heat in the first two cases is generally 

 of volcanic, or deep subterranean, origin ; but in the others it may come 

 from the oxidation of sulphides, or from other chemical action. 



When the temperature is high, the waters may be either approximately 

 pure, or strong mineral solutions. The waters often hold silica in solution, 

 whose deposition, over the region around, makes 

 irregular accumulations of a coarse opal, or rarely 

 of quartz, and forms low cones or rims about 

 basins. Occasionally, the waters are calcareous, 

 instead of siliceous, and make calcareous basins 

 or cones. The sources of such solutions, and 

 some of the effects resulting from them, are ex- 

 explained on pages 131, 135, and beyond. 



Geysers. — When a spring or basin of hot 

 water is in nearly constant ebullition, or is alter- 

 nately boiling and quiet, it is simply a hot spring 



or basin. But if the water is thrown up at nearly regular intervals, in jets, 

 it is called a geyser. Iceland has long been noted for its geysers, and the 

 theory of geyser action was there first investigated by Bunsen and Des 

 Cloizeaux. It has one great geyser in the vicinity of Hecla, among many 

 hot springs. The geyser sends up a great jet of 100 feet once in about 30 

 hours, and other smaller ones in the interval. The Icelandic word means a 

 " gusher." IN'ew Zealand has its geyser region, about Lake Eotomahana, in 

 the northern island, and had beautiful geyserite terraces until the volcanic 

 eruption of Tarawera in 1886, when mud eruptions buried them. 



Far exceeding either of these regions is the geyser area of Yellowstone 

 Park, first described by Messrs. Cook and Folsom in 1870, and by the Hayden 

 expedition in its volumes for 1871, 1872, and 1878, the last containing an 

 extended account by A. C. Peale. The region has since been further 

 studied and described by A. Hague, J. P. Iddings, W. H. Weed, and others. 

 The geysers are situated mainly about the Fire-Hole Fork of the Madison, 

 and near Shoshone Lake at the head of Lake Fork of the Snake. They 

 are exceedingly numerous, and play at all heights up to 200 feet or more ; 

 and, besides, there are multitudes of hot springs of various temperatures, 

 the most of them between 160° and 200° F., the boiling-point of the region 

 being 198° to 199° F. There are also " mud-volcanoes " where steam issues 

 through thick mud or muddy waters, producing, at times, ebullition, and 

 occasionally geyser action. The principal locality at the park is four miles 



DANA'S MANUAL — 20 



