the algae present a different development, forming leathery sheets of 

 tough gelatinous material, with coralloid and vase-shaped forms ris- 

 ing to the surface, and often filling up a large part of the pool. 

 Sheets of brown or green, kelpy or leathery, also line the basins of 

 warm springs whose temperature does not exceed 140° F., but in 

 springs having a higher temperature the only vegetation present 

 forms a velvety, golden-yellow fuzz upon the bottom and sides of the 

 bowl. This growth is rarelv noticed in springs where the water 

 exceeds 160° F., except at the edge of the pool. If the basin is 

 funnel-shaped, with flaring or saucer-shaped expansion, algse grow 

 in the cooler and shallower water of the margin, forming concentric 

 rings of yellow, old gold and orange, shading into salmon-red and 

 crimson, and this to brown at the border of the spring. Around 

 such springs the growth at the margin often forms a raised rim of 

 spongy, stiff jelly, sometimes almost rubber-like in consistency, and 

 red or brown in color. Evaporation of the water drawn up to the 

 top of such rims leaves a thin film of silica, which thickens to a crust 

 and so aids in the production of a permanent sinter rim." 



Near some springs, for example near the Emerald Pool, algal 

 channels are formed and the waterway is floored with a sheet of 

 olive or emerald green, kelpy jelly. Where there is a moderate 

 current, this lining is nearly smooth, resembling a sheet of wet 

 leather, but in quieter waters this soft carpet is dotted with little 

 warty excrescences, and little pillars produced by the upward growth 

 of the algae; the pillars sometimes terminate by balloon-like caps 

 or globes containing bubbles of gas. When, by their upward 

 growth, these pillars reach the surface of the pool, they increase 

 rapidly in diameter, and form flat, cap-shaped formations which 

 sometimes merge into table-like expansions of quite peculiar form. 

 The continued growth of new pillars dams up the outlet, and the 

 water collecting forms shallow lagoons or pools of varying degrees 

 of temperature. As the temperature changes, the nature of the 

 growth changes, the bright-colored algous jelly forming the outer 

 covering of the pillars changes to light salmon-pink, and the sub- 

 stance itself becomes noticeably silicious, or forms a filmy web upon 

 the silicious centre. 



It has been for some time known that the hot springs of the 

 world support various growths of microscopic plants. Agardh and 

 Corda recognized and described such in the hot springs of Carlsbad, 



