246 GEOLOGICAL SUEVEY OF THE TEREITORIES. 



the mound, covering an area at least 40 feet across. Just behind the 

 mound, and at its immediate base, there is a hirge ornamented opening, 

 which partly fills before eruptions, but is emptied by them. Much of 

 the ejected water falls in such a way as to flow back to this reservoir, 

 so as to keep up the supply necessary to the eruptions. These occur 

 pretty regularly for some hours, at intervals of from 2 to 3 minutes, but 

 gradual]}' decline in force, until the supply of water becomes exhausted. 

 Then the geyser is silent for several hours, until all the crevices, as well 

 as the suriace-pools, are again filled with water, when its eruptions 

 recommence with much violence, the jets then reaching altitudes of 

 from 30 to 40 feet. These again decline, and the series of phenomena 

 is repeated. As water gets low, the back pool sometimes receives some 

 of the steam-pressure and spouts from 5 to 8 feet. At one point 

 on the top of the mound, there are some small sulphur-vents, which 

 seem to be entirely disconnected with the water-pipes, but maintain 

 conimunications of their own with the volcanic laboratory beneath. 



About 50 feet farther on, Shield Geyser has an ornamented mound 

 about 15 inches high, which incloses a shield-shaped opening, measur- 

 ing about 8 feet on each of two sides and 7 feet on the third, at the top, 

 but narrowing to 4 feet on each of the two sides and 3 feet on the third, 

 a little lower, at what was water-level when I measured it. This spouts 

 moderately at intervals of a few hours, but no special notes of its erup- 

 tions were taken. By its side its partner has an irregular opening 

 about 8 feet long and varying from 10 inches to 3 feet in width. These 

 vents exhibited no sympathy with Minute Man. Their temperature is 

 190°. 



Between Shield Geyser and the foot of the hill, Eosette Spring has a 

 triangular basin with sides of about 15, 20, and 25 feet, in whose shal- 

 low waters form many most perfect specimens of the beautiful thin- 

 leaved rosettes already described as occurring in the Fire-Hole Basin. 

 The muddy bottom of this spring contains much sulphur. 



A little rocky knoll intervenes between this and the Bulging Spring, 

 which every few moments gives vent to large bubbles of steam, which 

 raise a considerable part of its surface from 1 foot to 3 feet, with a 

 bulging sound like that of liquid escaping from the bung of an over- 

 turned barrel. 



Forty feet beyond, the Soap-Kettle keeps up a furious boiling of col- 

 ored water, more or less covered with foam, looking like dirty soap-suds. 

 Its basin is lined with a yellowish-brown deposit. This has probably 

 been a strong spouter, but now erupts only at long intervals, if at all. 

 Its mound is about 8 feet across, and is still 1 foot high, though disin- 

 tegrating. 



Forty yards farther, the Black Sulphur Geyser has three vents, in 

 small dark-colored mounds, which almost constantly spit, but do not 

 spout much. An abundant black suli)hurous deisosit is formed along 

 the run from these.vents. 



The Twins are two small symmetrical vents, from 4 to G inches across, 

 in a small mound which stands back against the foot of the hill. They 

 spout rarely and to but small elevations. 



Several boiling springs occur at short intervals along the bottom. 

 About seventy yards farther on, a flat mound includes two large flat 

 openings which spout to the height of from 20 to 30 feet at short inter- 

 vals ; temperature, 192°. Above this point, the springs are of little 

 importance, though a few vents and old deposits occur at intervals for 

 a mile or two up the valley. One, near those last described, is a nar- 



