Page:Popular Science Monthly Volume 25.djvu/518

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One point which attracts attention, when the maps of these three regions are compared, is, that in each the hot springs appear to be associated with lakes. In Iceland there are six, in New Zealand fifteen, and in the Yellowstone Park four. All are of considerable size—Lake Taupo, in New Zealand, is twenty-five miles long by twenty wide; Yellowstone Lake measures twenty miles in length, by an average width of about eight miles. In Iceland, Hvitarvatn is nearly ten miles by eighteen; and Thingvallavatn has a length of about twenty miles, and a greatest width of ten or twelve miles. It is interesting in this connection to note that the Thibet geysers occur near a lake. Another point of resemblance is in the character of the deposits, which are alike in appearance, structure, and chemical composition, with the exception, perhaps, of some of the minor constituents. Silica is the predominant element in them, and is derived from the prevailing rocks. In the following table are some comparisons on these points:

LOCALITY. Grains of
silica to
a gallon of
of silica in
deposits from
Character of rocks. Percentage
of silica
in rocks.
Iceland 21·70 to 37·80 84·43 to 98·00 Palagonite and phonolite 41·28
New Zealand 11·48 to 43·95 77·35 to 94·20 Rhyolite and trachytes 70·0
Yellowstone Park 7·84 to 53·76 73·00 to 92·64 Obsidian and quartz-trachytes 64·60 to 77·90

The waters of New Zealand contain a much larger percentage of sodium chloride (common salt) than is found in those of the Yellowstone Park, or in the springs of Iceland.

The springs and geysers of New Zealand can be grouped in three parallel lines, and a similar linear arrangement is seen in the Yellowstone Park, and appears to be analogous to the linear arrangement so frequently noted in the case of volcanoes.

The plateau upon which the Iceland geysers is situated is surrounded on three sides with glaciers. In the Yellowstone Park, glaciers are things of the past; to-day only the erratic bowlders and scratches in the Yellowstone Valley testify to their former presence. In New Zealand the atmosphere is humid, and favorable to a growth of vegetation not found in either of the other regions. In New Zealand there are springs of greater size than those of either Iceland or the Yellowstone Park. In neither of the latter is there a hot lake like Rotomahoma, which is a mile wide by a mile and a quarter in length, and has an average temperature of 78° Fahr. The largest springs at present in the park are the Grand Prismatic spring, measuring two hundred and fifty by three hundred and fifty feet, and the small hot lake in the Lower Firehole Basin, which is one thousand feet long by seven hundred and fifty feet in width. In the past, however, the whole Lower