348 GEOLOGICAL EXCURSION TO THE ROCKY MOUNTAINS. 



mountain glacier. The Hotel terrace is the broadest of all the terraces, 



with an area over 83 acres in extent. It is situated 500 feet above the 

 river and from it most of the others are in full Bight. All active 

 springs are found either upon the Hotel terrace or upon those higher 

 up the valley. The number of active springs may vary from year to 

 year, some becoming extinct, while new vents are opened. The tem- 

 perature of the springs ranges from 80° to 165° P., in all of which 

 alga' have been found growing. This peculiar vegetation plays an 

 important part in the formation of travertine by the secretion of lime, 

 and much of the exquisite beauty of the springs and brilliancy of color- 

 ing is produced by these low forms of plant lite.' 3 



The principal objects of interest are the extinct springs, Liberty Cap 

 and tin' Thumb, on the Hotel terrace, and such active springs as Pulpit 

 Basins, Marble Basins, and the Blue spring, on Main terrace, and still 

 higher Cleopatra's Bowl, Cupid's Cave, and the Orange spring. There 

 are also innumerable small caves and fissures, each having special lea 

 turesof interest; some of the caves contain carbon dioxide in sufiieient 

 quantity to be dangerous to animal life. The largest active springs are 

 centered on Main terrace, 8f acres in extent and 250 feet above Hotel ter- 

 race. Beautiful clear pools abound, the largest of which is nearly LOOfeet 

 in diameter, with a temperature of 136° P. Blue spring on this terrace 

 is perhaps the most interesting of all in its phenomena of travertine 

 deposition. The building up of travertine in a series of small basins, 

 one above the other, the delicacy of coloring from algous growth, and 

 the overtlow of hot water are admirably shown. The spring has a tem- 

 perature of 1G5° P. 



Over the greater part of the travertine area hot springs have long 

 since ceased to tlow, although they may break out anew at any time. 

 Where they have long lain dormant, the spring deposits are now cov- 

 ered by a coniferous forest. In some instances the trees have been 

 killed by fresh outtlows of hot water, the dead and bleached trunks still 

 standing with their roots buried in travertine. 



Sepulchre mountain, to the northwest of Mammoth Hot springs, 

 stands out boldly as a volcanic peak, on the northern boundary of the 

 Park. It consists of Hows of compact andesite and breccias stretching 

 in long gentle slopes toward the Yellowstone and Gardiner rivers. 

 These spurs exhibit a succession of ice-carved benches, the surface 

 being strewn with glacial debris from the Gallatin Mountains. 



Mount Kvarts on the east and Terrace mountain on the west shut in 

 the Mammoth Hot springs on two sides, the former by a bold wall 

 rising abruptly above Gardiner river and the latter by long gentle 

 slopes inclined toward the river. Facing the basin on the south rises 

 a grand escarpment of volcanic rocks, the northern edge of the Bark 

 plateau, stretching from the head of Lava creek westward as far as 



