. Algæ. Vol. I. Myxophyceæ, Peridinieæ, Bacillarieæ, Chlorophyceæ, together with a brief summary of the occurrence and distribution of freshwat4er Algæ . s one of the most activespecies in building up calcareous deposits, and suchdeposits generally exhibit a well-marked zoning (). The Algae of hot-springs often grow as gelatinousmasses in which a glassy form of silica graduallyappears, and ultimately all except the peripheralportion becomes firmly silicified. Weed found thatthe thickness of travertine formed in three daysvaried from 1*25 to 15 mm. He also found that thecharacter and colo
. Algæ. Vol. I. Myxophyceæ, Peridinieæ, Bacillarieæ, Chlorophyceæ, together with a brief summary of the occurrence and distribution of freshwat4er Algæ . s one of the most activespecies in building up calcareous deposits, and suchdeposits generally exhibit a well-marked zoning (). The Algae of hot-springs often grow as gelatinousmasses in which a glassy form of silica graduallyappears, and ultimately all except the peripheralportion becomes firmly silicified. Weed found thatthe thickness of travertine formed in three daysvaried from 1*25 to 15 mm. He also found that thecharacter and colour of the deposit depended verylargely upon the temperature of the water and thesituation of the spring or geyser. The highesttemperature at which Myxophycese have been foundis 875°C., at which temperature Phormidium laminosum has been stated tooccur. In the spray of a small geyser at Hveravellir in Iceland, Phormidiumangustissimum, Ph. tenue, and Mastigocladus laminosus were thriving (G. S. W.,02). The temperature of this spray was 85° C., but it is highly probable thatit would be so rapidly reduced that the wet stratum of the Algae would be at. Fig. 21. Photograph of asection through a frag-ment of a calcareousnodule built up by Diclio-thrix gypsopliila (Kiitz.)Born. & Flah. Naturalsize. Note the well-marked zoning. Symbiosis 35 a temperature of possibly 10° less. Of the , Aphanothecethermalis Brugger and A. bullosa, Rabenh. have been observed living inwater at a temperature of 6<S75° C. On the whole, it may be said thatno organisms, with the possible exception of certain Bacteria, possess sucha capacity as the Myxophycere for withstanding extremes of temperature. Myxophycetp of the genera Gloeocapsa and Gloeothece are responsiblefor the formation of oolitic calcareous grains on the shores of the GreatSalt Lake, Utah, and white grains of a similar kind are known from theRed Sea. On the bottom of Lough Belvedere, near Mullingar in Ireland,numerous s
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