(illy, 

 igso 



Shkaksev. Recoil Traverliti FonnaHotis. Yass. 37 



described * a remarkable occurrence" of a mass of incrusted 

 plants of the lime-secreting Chara, filling up an old pool near 

 Northampton. 



How perfectly the impressions of vegetable matter may he 

 retained by the incrusting substance can be realized from the 

 description given by Prof. Seward f of a porous calcareous rock 

 of Eocene age near Sezanne, Southern France, formed of 

 encrusted leaves, twigs, and flowers ; these have been restored 

 to their original delicate shapes by forcing wax into the 

 cavities and dissolving away the tufa. 



The travertin deposits near Geilston and Hobart, Tasmania, 

 described by Johnston, J were also formed in lakes fed by cal- 

 careous springs, and the leaves which were washed into them 

 {Notojagiis Risdoniana) are beautifully preserved as impressions. 



In some ways allied to tufa deposits is the phenomenon of 

 the lime-incrusted stems and roots of the Coast Tea-tree 

 {Leptospermiim Icpvigatmn), which in later stages become 

 solidified by deposits of carbonate of lime from solution. This 

 has engaged the attention of observers from the time of 

 Vancouver (1791), and Darwin (1836) commented upon it. 

 As Dr. T. S. Hall pointed out § in his valuable paper on this 

 subject, it remained for Moseley, j! of the Challenger expedition, 

 to explain the actual facts respecting the formation of this 

 coastal tufa, which, unlike most other deposits, seems to be 

 dependent on the acids derived from the decay of the vegeta- 

 tion itself in its reaction on the calcareous shore-sand. 



The older groups of rocks, of the ages of Silurian, Devonian, 

 and Triassic, contain limestones of algal and other plant origin, 

 but their age and consequently greatly altered mineral con- 

 dition often precludes a very close analogy with the modern 

 deposits of like origin, although in certain instances conspicuous 

 intercalations of calcareous tufa can be clearly seen. Thus, 

 the Upper Devonian of Freestone Creek, Gippsland, contains 

 a typical tufa deposit which is associated with plant-bearing 

 sandstones. 



In the study of agencies which produced any geological 

 formation, it is of the greatest value to obtain evidence of 

 similar conditions taking place at the present time, and such 

 an instance as Mr. Shearsby has so well described and photo- 

 graphed makes us familiar with the actual mode of formation 



* Geol. Maq.. vol. v., 1868, p. 563. 



■{•"Fossil Plants," vol. i., 1898, p. 70. Also Saporta, Mem. Soc. Clcol. 

 France, vol. viii. (2), 1865-8. 



I Geol. Tasmania, 1886, p. 286. See also Proc. R. Soc. Tas. for 1879 

 (1880), p. 81 ; 1881 (1882), p. 7. 



§ Victorian Naluralisl, vol. xviii., 1901, p. 47. 



II " Notes by a Naturalist on the Voyage of H.M.S. Challoi^er." p. 149. 



