GEOLOGICAL HISTOKV OV THE YELLOWSTONE PARK. 145 



there was iiii abmulant sepaiatioii of tVec silica. The waters frozen in 

 this way Avere eoHeeted from the ('oral Spriiiy, Norris r>asiii, and the 

 Taurus (Tcyser, Shoshone Basin. 



Ag'ain, there is no (h)ul»t that the al,ii'ous growths found th»urishing 

 in the hot waters of the Park favor the secretion of silica and exert an 

 iutluenee in buildiug* np the geyserite far greater than one would at 

 tirst be led to suppose. These low forms of vegetable life occur in 

 nearly all ])ools, springs, and running waters, up to a temperature of 

 185° F. (only lo° beh)w the boiling point), at the Upper (Jeyser Basin. 

 If time permitted, much might b(i said on this subject. I will only add 

 that Mr. Walter PI. Weed, in eonnection with his other duties on the 

 Geological Survey, has devoted much tiuje to a study of these algous 

 growths, and the results of his investigations will form an important 

 chapter in the linal publications. 



Several methods have been devised for ascertaining the growth of 

 deposition of the geyserite. One way is by allowing the water to 

 trickle over twigs, dried grasses, or almost anything exposing consid- 

 erable surface, and noting the amount of incrustation. This way 

 gives the most rapid results, but is far from satisfactory and by no 

 means reproduces the conditions existing in nature. Other methods 

 employed are i)lacing obje(;ts on the surface of the water or, still 

 better, partially submerging them in the hot ])ools, or again by allow- 

 ing the water to run down an inclined plane with frequent intervals 

 for evaporation and concentration. 



The vaiulals who deliglit to inscribe their names in publi<' places 

 have invaded the geyser basins in large numbers and left their 

 addresses upon the geyserite in various places. It is interesting to 

 note how ([uickly these inscriptions beconu' indelible by the deposition 

 of the merest lilm of silica upon the lead-Dcncil marks, and, at the 

 same time, how sh)wly they build up. Names and dates known to be 

 six and eight years old remain ])erfcctly legil)h', and still retain the 

 coh)r and luster of the graphite. That there is some increase in the 

 thickness of the incrustation is evident, although it grows with 

 incredil)le slowness. Mr. Weed tells me that he has been able, in at 

 least oiu', instancM', to chip olf this siliceous tilm and reproduce the 

 writing with all its original distinctness, showing conclusively that a 

 slow deposition has taken place. I*encil inscriptions upon the sili- 

 ceous sinter at llotomahana Lake, in New Zealand, are said to be 

 legible after th(^ hi))se of twenty or thirty years. It is easy to see 

 that various ingenious <levices might be planned to estimate the rate 

 of dei)osition, ])ut in my oj)inion none of them e(pial a close study 

 of the conditions found in nature, especially wheie investigations of 

 this kind can be watched from year to year. All observations show 

 an exceedingly slow building up of the geyserite formation. Tiiis is 

 Avell seen in the repair going on where the rims snri'ounding tlu^ hot 

 pools have been broken down, and where it might be supposed that 

 H. Mis. 114 10 



