360 GEOLOGICAL EXCURSION TO THE ROCKY MOUNTAINS. 



THE FORMATION OF HOT SPRING DEPOSITS.-' 

 By Walter 11. Wxbd. 



Travertines-Tile travertine deposits of the Mammoth Hot springs 

 form one of the most interesting features of the region. Covering two 



square miles and attaining a thickness in places of 250 feet, the deposits 

 have few equals in size, while the beauty Of the terraced basins, the 

 brightly tinted slopes covered by the steaming waters, and the varied 

 views presented can not fail to impress every observer. 



With the except ion of the Hot River, all the active springs now issue 

 from the terraces above the hotel; elsewhere the older deposits are 

 quite generally covered by a forest growth of pines and spruces. In 

 wandering about the springs one is sure to notice the brightly tinted 

 basins surrounding the vents, with the red or orange colors of the 

 slopes overflowed by the hot waters. These colors are due, not to 

 mineral matter, but to the presence of algffl growing in the hot waters 

 and frequently so covered by carbonate of lime as to be scarcely recog- 

 nizable. These plants take a most important part in the formation of 

 the travertine deposits, and in fact it is their presence that has caused 

 the great beauty of the deposits. The varied tints are due to a differ- 

 ent eolor of the alga; at varying temperatures, examples of which are 

 seen in the beautiful mosaic of basins about the vents of the Bine 

 springs on the Main terrace. 



The fact that these deposits of travertine are mainly due to plant 

 life has been fully proven by a careful study of the old deposits and of 

 those now forming. This action of alga- was first observed by Ferd. 

 Cohn at Carlsbad and other European localities, and the study of the 

 \ellowstone deposits simply extends and confirms his theory. The 

 proof is readily available at the Mammoth Hot Springs, and, though 

 other causes cooperate to produce a separation and deposition of the 

 carbonate of lime from the hot waters, the plant life is seen to be the 

 chief factor in the production of the many varieties of calc sinter found 

 about the springs. In the case of the fibrous tufa forming the fan- 

 shaped masses found about many of the vents, an examination with a 

 lens shows that the fibers are simply encrusted alg;e threads. The 

 rippled surface of the deposits covered by the overflow of the larger 

 springs shows a furry covering of orange-colored alga-, the upright 

 threads extending down into the mass. In both these cases the algffi 

 filaments serve as a nucleus for encrustation, besides absorbing carbon 

 dioxide and thus causing the separation of lime carbonate. The 



