266 OCCURREXCE OF DIATOMACEOUS EARTH, 



in this deposit, as I understand that this is a work which has 

 already been commenced by Mr. W. kS. Dun and Mr. G. W. Card, 

 and an interesting paper from them on this subject may shortly 

 be expected. .1 would merely add that Melosira appears to 

 greatly predominate among the Diatoms, but not to the entire 

 exclusion of other forms. The sponge spicules are a cerate or 

 fusiform, slightly arcuate, and some are thorny, but the majority 

 smooth. 



I should like to emphasise the fact that hitherto all our diato- 

 maceous earths in New South Wales have been found in associa- 

 tion with volcanic rocks, and I would venture to suggest that this 

 association is probably far from accidental. The superheated 

 Avater flowing from hot springs and from the lavas themselves 

 during the trachytic eruptions would be certain to carry more or 

 less silica in solution, and its high temperature, combined with 

 its dissolved silica, would probably render it a very favourable 

 medium for the development of Diatoms to the exclusion of most 

 other kinds of plant. While some species of Diatoms flourish 

 luxuriantly in the cold waters of the Antarctic Ocean, others may 

 be found equally flourishing in the hot and highly mineralised 

 waters of geysers. For example, Mr. H. N. Moseley* has described 

 the occurrence of Diatoms near the Boiling Springs at Furnas, St. 

 Michael's, Azores, and their neighbourhood. 



Mr. Moselej^ states (op. cit. p. 322) " The Chroococciis ^Botryo- 

 coccus Braunii , Ktz., as would appear from the footnote. T. W.E. D.] 

 was not so abundant in the samples of incrusting matter in this 

 hot spring as in those from the spring at Furnas. Amongst the 

 green matter are a few skeletons of Diatomacete (a Nuvicnla); 

 but these are very probably derived from a cool spiking, 

 situate just above the sulphur spring, the water of which 

 mingles with that of the sulphur spring, and indeed appears 

 to supply a large share of the water of most of the hot springs, 

 the water being merely heated and impregnated with various 



* Joiun. Linn. Soo. Bot. Vol. xiv. p. 322. 



