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



sinter produced byalgas, a striking illustration of the proportion 

 of algous sinter of such deposits, while the remaining two feet 

 consist principally of the cemented fragments of the same 

 varieties of sinter. This preponderance of algous sinter in the 

 deposits of all the geyser basins (save the Norris basin), is due 

 to the greater rapidity with which it is formed. 



Mate of formation. — Excepting the deposits formed by 

 the highly charged waters of the N orris Basin, which deposit 

 silica very rapidly, the hot spring and geyser waters deposit 

 silica very slowly, by causes other than vegetable life. The 

 beaded deposits which characterize the vents of the geysers, 

 and to which the name geyserite is most properly applied, are 

 formed entirely by evaporation. It is of course difficult to 

 make any estimate of the average rate at which such deposits 

 are formed about the older geysers. Quite recently, however, 

 the development of a quiet " laug" a non-boiling spring, into 

 a geyser named the Liberty has afforded an excellent opportu- 

 nity for the study of the rate of formation of this class of sin- 

 ters. A careful examination shows that an average thickness 

 of /o of an inch has been formed in the eighteen months' activ- 

 ity of this vent. The laminated sinters about many of the 

 springs are less rapidly formed. At the Model Geyser, under 

 very favorable conditions for the formation of sinter by evapo- 

 ration, i. e., alternate wetting and drying of the surface, a 

 deposit formed over a name written upon the surface of the 

 sinter nine years ago, and known to be authentic, is but T \-§ of an 

 inch thick, while more recent names are glazed with a coating 

 of silica of extreme thinness. The salmon-colored floor of a 

 channel near the Castle geyser is liberally inscribed with names 

 of visitors, and although marring the beauty of the deposit they 

 furnish a record of the rate at which the sinter forms at this 

 place. In this case, moreover, the salmon -pink color is due to 

 the presence of a fuzz of algse, so that a coating of T ±o to -^ of 

 an inch a year, is not due wholly to evaporation. 



The fibrous sinter forming the floor of the channels of Old 

 Faithful is composed of layers, whose average thickness is -^\ of 

 an inch, separated by lines of dense glassy silica. Each layer 

 probably represents a summer's growth, and the annual thick- 

 ness formed at this place can scarcely exceed ^ of an inch. 



The algous jellies, however, grow very rapidly — a thickness 

 of four to five inches forming in several months under very 

 favorable conditions, and a thickness of 1|- inches in 2£ months 

 by actual experiment. Such jellies, deprived of the necessary 

 supply of water, soon harden, and a crust forms on their sur- 

 face by evaporation so that a considerable thickness of this 

 form of sinter may be produced in a comparatively short time; 

 by this agency. 



