1876.] Geology and Paleontology. 243 
‘spring the spurting of the liquid, when it occurs, is owing to a resist- 
ance offered to the direct escape of the expansive force from below, and 
this resistance may be found in the tenacity of the liquid contents of the 
bowl, in the untoward shape of the bowl or its connected passages, or in 
the sudden restriction of the orifice near the surface of the liquid. In 
either case the uprising force is condensed, as it were, near one point, 
and the spurt or eruption is caused by the sudden overcoming of the ten- 
sion when the force has become sufficiently concentrated to free itself 
from its confinement. Thus we may meet with a great variety of spout- 
ing thermal springs, resulting from two or more of these causes com- 
_ bined, and the force may be produced by heat alone or by the evolution 
of carbonic acid or other chemical change in addition. (See F igure 14.) 
he channel is con- 
The arrows Tepresent the direction of the action of the subterranean force. 
stricted at o o, the entrance of the surface bowl; 1, 2,3 represent the variable position of the suc- 
cessive jets, 
“The phenomena observed in connection with the typical geyser, how- 
ever, do not admit of such a simple explanation; and there is much 
doubt whether existing theories are sufficient to account for all the com- 
mon manifestations of such agitated bowls. Almost without Sereno, 
in the true geyser, the action, whether frequent or the Peyvetee, 16 miter: 
mittent, although the successive periods in each case may be quite irreg- 
ular, Usually, as the first indications of an approaching eraption, there 
Will be noticed an escape of vapor, soon followed by a sudden rising of a 
mass of water sufficient to fill the surface-chamber of the geyser. The 
Phenomena which follow are very largely the result of structural features 
0f varying nature, no doubt, but it will invariably be found that the 
eruption takes place near the centre of the bowl, and that the elevation 
of the column of water is accomplished by continuous or successive 
throes from one Spot, while in the ordinary eruptive springs the column 
' seldom shot upward from the same point twice in succession. We 
