351 W. II. Weed — Formation of Siliceous Sinter. 



Algce sinter. — This action of plant life consists in the abstrac- 

 tion of silica from the hot spring waters, by the vital processes 

 of the algous vegetation, and in its deposition as a stiff gelat- 

 inous substance, occurring in a great variety of forms. This 

 material, seemingly an inorganic deposit of gelatinous silica, con- 

 sists of the siliceous filaments of various species of algae, and 

 their slimy envelope. Upon the death of the algae this jelly 

 loses part of its water, becoming cheesy in consistency and 

 gradually hardening, and with a further separation of silica 

 owing to the action of the decaying vegetable matter upon 

 the water, it becomes a hard stony mass of sinter. If, however, 

 a mass of the algous jelly be removed from the water and 

 dried in the sun, it becomes a very light, pinkish material, 

 containing about 94 per cent of silica, three to four per cent 

 of water and one to two per cent of organic matter, with a 

 little alumina — showing it to have the composition of a very 

 pure siliceous sinter. 



That vegetable life can exist in highly heated waters is well 

 known to botanists. In the Yellowstone springs the maximum 

 temperature at which vegetable life has been found is 185° F. ? 

 only 13 degrees below the boiling point at this altitude, and 

 algous growths are very common in the alkaline waters of the 

 Geyser Basins — forming a brilliant and beautiful feature of the 

 springs and their deposits. With rare exceptions the yellow 

 and salmon tints of the geyser pools and the reds, orange, 

 greens and browns of the hot springs are produced by algous 

 vegetation. 



The clearest case of sinter formation by algous life is that 

 shown by a species of Lejitothrix, forming thick masses of 

 jelly, often assuming columnar, and vase-shaped forms, in the 

 areas overflowed by the Black Sand, and Emerald Springs, at 

 the Upper Geyser Basin. Here we have the conditions most 

 favorable for the development of this form, viz : a constant 

 volume and temperature of the overflow, and a gently sloping 

 surface. Under such circumstances the overflow area is first car- 

 peted with a membranous algous sheet, the color depending 

 upon the temperature. ,From this flooring warty excres- 

 cences grow upward into pillar-like forms of soft jelly, until, 

 reaching the surface of the water, their upward growth ceases, 

 and a lateral development results in the formation of a cap, or 

 " pileus " upon each pillar. These caps uniting, together with 

 the growth of new, and the thickening of older pillars, fill up 

 the channel and dam back the water, forming a little basin. Such 

 growths thus form a series of terraced pools, in which the 

 algae thrive or die according to the supply and temperature of 

 the water. In such basins one can see all gradations from the 

 slender spikes of soft jelly to the hard firm sinter into which 



