

256 RELATION OF PLANT PROTOPLASM TO ENVIRONMENT. 



Third. The formation of siliceous and calcareous sinters and their relation 

 to the Schizophyceous algae may next be considered. The striking observations 

 of Cohn (6) on the waters of Carlsbad, confirmed and extended by Weed (7) and 

 subsequent workers, show that whether in siliceous or in calcareous thermal 

 waters, definite species of the thermal algae are so able to act chemically on 

 dissolved constituents that the silica or the lime is precipitated in coarse colloid 

 molecules or granules. These gradually unite with each other to produce 

 agglutinated threads of gelatinous or colloid substance which collectively make 

 up the sinter. "Upon the death of the algae which have separated this jelly from 

 the spring waters, there is a loss of a large part of its water, and a change to a 

 soft cheesy, but more permanent form. This dehydration is carried still further 

 if the silica be removed from the water and dried, but if allowed to remain in the 

 cold water pools there is a further separation of silica, possibly due to organic 

 acids, formed by the decaying vegetation reacting upon the silica salts of the 

 water ; this hardens the existing structures, in certain cases, and generally covers 

 the pillars with a frost-like coating of silica. In general it may be stated that 

 the large vase and pillar forms found in the algal pools can be produced only by 

 the concurrent life and death of these plants, the outer layers continually growing, 

 the inner dying. This is readily seen to be the cause of the peculiar structure of 

 these forms. The central core is a pillar, sometimes hollow, sometimes solid, con- 

 sisting of thin superimposed layers of silica, each of which corresponds with a 

 layer of algal jelly, which has become hardened by the death of the plants and the 

 loss of water. The column increases in diameter by the growth of the algae at the 

 surface, and a simultaneous death and hardening of the inner layer of jelly." 



Over areas where the sinter is in process of deposition it is noticed, in the 

 more celebrated geyser regions of the world, that a striking variation in color 

 can usually be traced by the naked eye, and equally in the algae when closely 

 examined. The former give rise to those delicate but magnificent tints of color 

 that have impressed every visitor to the regions in question; the latter shade 

 from pale Beggiatoa forms that merge into elongated thread forms, through 

 yellow to yellow-brown, pink, pinkish-green, purple-green, and — along the cooler 

 margins of deposit— to deep emerald green. Reference will be made below to 

 this color relation. 



But no matter what the color species of alga be that precipitates the sinter, 

 this soon loses its color and assumes a dull gray tint for siliceous, or a pure white 

 hue for calcareous deposits. In regard to the after-relation of the algae to the 

 deposits Weed says: "The desiccation of such areas leaves a deposit of sinter 

 whose surface shows no trace of its origin and of the beautiful forms beneath." 

 This uniform opalescent character of the sinter deserves emphasis in connection 

 with what we will state below as to the possible occurrence of rock masses similar 

 in type and origin. 



Fourth. In treating of the fourth question it will readily be accepted, we 

 believe, that considerable though the area of hot spring activity now is, such is a 



