CLASSIFICATION AND COMPOSITION OF THERMAL SPRINGS 115 



inclined Jurassic limestones. The circulating hot waters having been 

 diverted in their course traverse the limestone before issuing at the sur- 

 face. Apparently the waters derive a large part of their mineral con- 

 stituents from the limestone. In contrast to the hot waters of the plateaus 

 they carry but little silica in solution. Far to the southward, where the 

 rhyolite tableland ends, the attenuated lava streams also rest against up- 

 lifted limestones. Calcic carbonate springs, although of modest dimen- 

 sion, issue through the rhyolite, but have derived their mineral contents 

 mainly from the adjacent limestones. Both the carbonated waters and 

 the travertine deposits resemble those at Mammoth Hot Springs. Similar 

 geological relations may be observed near the eastern limits of the rhyo- 

 lite at Soda Butte Spring, and again near the western border. 



On the other hand, wherever the heated waters issue from the rhyolite 

 of the tableland they are characterized by a high percentage of silica. 

 These waters occur distributed over a wide area and furnish the great 

 volume of water discharged from the geysers and hot springs, and for 

 this reason have excited more general interest than the smaller springs. 

 They have supplied the silica for the many square miles of glittering 

 white sinter plains. For the most part they are siliceous alkaline waters, 

 as in the Upper Geyser Basin and the Firehole Basin. They, however, 

 may be slightly acid or neutral, as in the case of many of them in Norris 

 Basin. 



The silica occurs in solution as hydrated silica associated with carbo- 

 nates and chlorides of the alkalies, together with small quantities of sul- 

 phates. Arsenic and boron have been determined in nearly all geyser 

 waters, probably combined with soda as arsenates and borates. Traces of 

 bromine, phosphoric acid, soda, manganese, lithium, caesium, and rubi- 

 dium were detected in several instances, but lithium and bromine are the 

 only elements present in sufficient quantities to allow of estimation. 

 Tests were made for titanic acid, nitric acid, iodine, fluorine, barium, 

 and strontium, but none of them were found. Special examinations 

 were made in concentrated solution for tin, copper, and lead, but no one 

 of them was present. In this connection it may be pointed out that while 

 veins carrying lead, copper, and silver are found associated with Eocene 

 and Miocene igneous rocks, these metals have never been detected in 

 either the rhyolite or waters of the park. 



A study of these chemical analyses brings out clearly the marked differ- 

 ences in percentages of substances held in solution, especially silica, even 

 in adjoining geysers. This holds equally well for the siliceous alkaline 

 waters from the same geyser basin as from those collected from different 

 localities. Waters examined the same year show as great variations as 

 those collected one or two years apart. The silica, as determined by 



