LW? GEYSERS. 
the waters excludes this theory. The folding and faulting of rocks is 
another source of heat made manifest by hot springs. 
It has been shown by Dr. Peale, however, that boiling waters are only 
found in the regions of volcanic rocks, and it was pointed out by L’Ap- 
parent that geysers only occur in acid voleanic lavas. In Iceland the 
volcanic forces are still active, and melted lavas may exist at no great 
depth. In New Zealand the recent eruption of the eroded mountain 
Tarawera showed that heated rocks exist, and in that case rose up 
near enough to the surface to cause the explosion which so trans- 
formed the country. 
In the Yellowstone there are no active voleanoes, and none of even 
geologically recent activity. The lavas that fill the ancient mountain- 
encircled basin of the park are scored by glaciers and deeply cut by 
running water; and the old volcanoes from which the lavas were, in part 
at least, outpoured show no signs of having been active since Tertiary 
times. Yet in this region the expenditure of heat by the hot springs, 
geysers, and steam vents would undoubtedly keep a moderate-sized 
volcano in a very active state were it concentrated. There is no doubt 
that this heat is connected with the past voleanic energies of the region 
and derived principally from the still hot lavas, three-quarters of the 
entire area of the park (3,500 square miles) being covered by rhyolitie 
rocks. 
The significance alluded to above, of the association of geysers and 
acid lavas (rhyolites), is possibly to be found in the fact that these rocks 
are more easily dissolved by the hot waters forming the tubes and res- 
ervoirs for geysers. The situation of hot springs and geysers along 
water courses has already been mentioned. Itis a well-known fact 
that the presence of water in the pores of a rock increases its capacity 
to conduct heat, so that we may surmise a rise in the local isogeotherm 
in such situations. 
Geyser eruptions.—Geysers have often been compared to volcanoes, 
presenting in miniature, with water instead of molten rock, all the phe- 
nomena of a volcanic eruption. The diversity of form and varying con- 
ditions of activity of the hot springs found associated with geysers 
makes it impossible to determine in every case whether a spring is 
or is not a geyser. Geyser vents may be mere rifts in the naked rocks 
or bowls of clear and tranquil water, quiet until disturbed by the first 
throes of an eruption, and surrounded by white sinter deposits in nowise 
distinguishable from those about hot springs. In other cases the vents 
are surrounded by a cone or mound of pearly-beaded “ geyserite,” a 
certain and distinctive feature of a geyser. 
The displays of the great “Geyser” of Iceland have already been 
briefly described; they may be taken as the type of eruptions from gey- 
sers having bowl-like expansions at the top of the tube, the so-called 
“basin” of the geyser. Where the vent is surrounded by a cone of 
Sinter, as is so often the case among the fountains of New Zealand and 
