504 



THE POPULAR SCIENCE MONTHLY, 



One point which attracts attention, when the maps of these three 

 regions are compared, is, that in each the hot springs appear to be as- 

 sociated 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. An- 

 other 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. 



Iceland 



New Zealand. . . . 

 Yellowstone Park 



Grains of 



silica to 



a gallon of 



water. 



21-'70 to 37-80 



11-48 to 43-95 



7-84 to 53-76 



Percentage 



of silica in 



deposits from 



waters. 



84-43 to 98-00 

 77-35 to 94-20 

 73-00 to 92-64 



Character of rocks. 



Palagonite and 

 phonolite 



Rhyolite and 

 trachytes .... 



Obsidian and 



quartz-trachytes 



Percentage 

 of silica 

 in rocks. 



41-28 

 723 



70-0 

 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 Yellow- 

 stone 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 Yellow- 

 stone 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 surround- 

 ed 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 vegeta- 

 tion not found in either of the other regions. In New Zealand there 

 are springs of greater size than those of either Iceland or the Yellow- 

 stone Park. In neither of the latter is there a hot lake like Rotoma- 

 homa, 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 hun- 

 dred and fifty feet in width. In the past, however, the whole Lower 



