PROCEEDINGS OF THE COTTESWOLD CLUB 261 



It is in this way that the stony deposit or " fur " found 

 in boilers and kettles containing hard water, such as is 

 supplied to Gloucester, is produced. 



From the same cause arise all the massive and beautiful 

 travertine deposits of the Mammoth Hot Springs on 

 Gardiner River, near the Northern boundarv of the Park 

 [lantern slide shown], which cover an area of several 

 square miles, forming a series of terraces of great thick- 

 ness, edged with stalactites in every variety of form. 



But the Geysirs of the Firehole River form deposits of 

 totally different chemical character, though equally beauti- 

 ful and diversified in form, consisting of verv pure silica ; 

 or rather, silicon hydrate, since they all contain the 

 elements of water. The history of these formations is the 

 following. The volcanic trachytes and basalts already 

 described consist of various and complex silicates, contain- 

 ing silicon and oxygen united with the basic radicles 

 aluminium, iron, potassium, and sodium. These com- 

 pounds all break up more or less readily under the 

 influence of heat and moisture into clay (aluminium 

 sihcate), iron oxide, salts of potassium and sodium, and 

 silica. The clay, which is, for the most part, very pure, 

 white kaolin, and might be used for making porcelain and 

 china ware, forms the solid ingredient of the mud 

 volcanoes or " paint-pots " as they are rather clumsily 

 termed. The iron oxide contributes the colouring 

 matters, — brown, red, and green, — which add so much 

 to the beauty of the geysir deposits ; while the silica 

 under the influence of the subterranean heat and pressure, 

 combines with the alkaline salts to form soluble potassium 

 and sodium silicates resembling the common "water-glass" 

 of which I exhibit a specimen. This latter dissolves in 

 the hot water of the geysirs, and the sihca is deposited, as 

 the solution cools and evaporates, in verv beautiful and 

 often fantastic forms ; giving not only the vast thick 

 sheets, mounds, and spouts of the geysirs, but also the 

 R 



