358 W. H. Weed — Formation of Siliceous Sinter. 



The numerous analyses of sinters, made in the Survey Lab- 

 oratory, show that those formed by mosses and algous vegeta- 

 tion are generally purer than the true geyserite, the latter con- 

 taining more or less clay, resulting from particles in suspension 

 in the geyser waters. The algous sinter does not differ in com- 

 position from the opal sinters produced by the waters of the 

 Coral and other springs at the Norris Basin, nor from the 

 purer geyserites formed by evaporation. 



Siliceous Sinter from New Zealand. 



Through the courtesy of Prof. F. W. Clarke I have been 

 enabled to examine a small collection of New Zealand " geyser- 

 ites " and to compare them with the Yellowstone sinters. The 

 specimens are mainly from the hot springs of Rotorua (or 

 Ohinemutu), where the waters, long used by the Maori for 

 cooking and bathing, are now utilized for a government sanita- 

 rium. 



The collection embraces a number of varieties of sinters : 

 true geyserites, formed by the evaporation of spattered drops 

 of water ; incrustation sinters, resembling a crushed handful of 

 hay converted into silica ; opal sinter and hot spring sandstones. 



Besides these varieties there are two specimens whose struc- 

 ture indicates that the algous vegetation of the New Zealand 

 waters produces siliceous sinter. These specimens are, however, 

 quite unlike ; the first resembles the sinter resulting from the 

 growth of membranous sheets of red or green algse, a form of 

 vegetation resembling certain species of sea- weeds. Such algous 

 sheets occur in hot waters all over the globe, and are described 

 as " sheets of a slimy confervoid growth " * in the Rotorua wa- 

 ters. The sinter is creamy pink, showing a wavy, very thinly 

 laminated structure, with occasional vesicular blisters lined 

 with red and green patches, presumably the remains of algse. 

 It so very closely resembles sinters, whose algous origin is 

 known, that a similar origin seems probable. An analysis of 

 this specimen is given in the table following. 



The second specimen is quite different in structure, consist- 

 ing of several layers of fibrous silica, the fibers all perpendic- 

 ular, and resembling a very fine, short and thick white fur. 

 This sinter is exactly like the algous sinter forming the floor of 

 the channels of the Old Faithful geyser and making one-half 

 of the section of 12 feet of sinter exposed in the walls of the 

 Excelsior, and there seems no reason for doubting that it has 

 been formed in the same way. 



The following analyses of New Zealand sinters have been 

 made by Mr. J. Edward Whitfield, of the Survey Laboratory. 



* Skey, Trans. N. Z. Inst., vol. x, p. 433. 



