270 Professor E. J. Gariuood — Rock-building Organisms. 



concentrically with specimens of Ortonella and Aphralysia (PI. XXI, 

 Figs. 3, 4). Under the microscope no definite cell-structure can be 

 made out, and the general appearance is that ol: an indefinite 

 flocculent precipitate of carbonate of lime which has the appearance 

 of having been thrown down from solution as the result of the 

 abstraction of C Og from water containing calcium bicarbonate in 

 solution. The character of these structures, coupled with the general 

 absence of definite mechanical and organic fragments, where they 

 occur, points strongly to their organic origin, while their constant 

 association with Ortonella, Mitcheldeania, and Solenopora would 

 suggest that the conditions under which they were formed were of 

 a lagoon character suitable for the growth of marine algae. At the 

 same time the absence of definite cell-structure suggests that they 

 represent the insoluble Ca C Og precipitated in an amorphous condition 

 as the result of absorption of C Og from the water by growing plants 

 rather than definite structures built up in the cells of calcareous algae.' 

 General precipitation of this kind is well known to botanists at the 

 present day. Thus the famous ' Sprudelstein ' of Carlsbad has often 

 been stated to have originated in this manner, though this has 

 been disputed by some recent observers. There cannot, however, be 

 any doubt regarding the action of certain plants in this connexion. 



During the progress of the bathymetrical survey of the Scottish 

 lochs, abundant precipitation of calcium carbonate, due to plant 

 action, was observed. In addition to lime-encrusted CharaceES in the 

 lochs of Lismore, lime-encrustations were observed on the stones of 

 the shore formed by minute lithophilous algse, in the process of their 

 metabolism, while certain plants such as Myriophylhim spicattim and 

 Potamogeton were found to produce heavy precipitates of Ca C Og. 

 The former plant is stated by Mr. George West- to be so heavily 

 coated with encrustations of carbonate of lime that the plants are 

 often unable to rise to the surface for the purpose of pollenization. 

 Were it not for the fact that the majority of the Scottish lochs 

 lie in areas where the rocks are practically devoid of lime, this 

 phenomenon would doubtless have been met with more frequently. 



In the Swiss lakes also (Geneva, Neuchatel, etc.) the blue-green 

 algae, according to Chodat, cause important precipitation of Ca C Og. 

 Indeed, in recent years there has been a growing conviction among 

 writers on lake deposits (C. A. Davis, ^ Wesenburg-Lund,* Weltner,* 

 Passarge,^ and others) that the lime deposits in lakes are chiefly, if 

 not entirely, due to organisms, among which plants often play a very 

 important part. It seems highly probable, then, that similar amorphous 

 deposits are also taking place in shallow seas, especially where 

 lagoon conditions prevail and algae flourish. Our knowledge of such 



^ Thus, if water is saturated with calcium bicarbonate, then for each gram of 

 C O2 abstracted by plants, 2'3 grams of Ca C O3 are precipitated. 



^ Bathymetrical Survey of the Fresh-water Lochs of Scotland, vol. i, p. 213,. 

 1910. 



* Journal of Geology, Chicago, vol. viii, p. 485 ; vol. ix, p. 491. 



^ Meddel fra Dansk Geolog. Foren. Kobenhavn, vii, 1. 



® Archiv f. Naturges., vol. Ixxi, p. 277. 



'' Jahrb. d. Konigl. Preuss. Geol. Landesanst, vol. xxii, p. 79. 



