CHARA MARLS; FOSSIL OOLITES 471 



The nullipores are often the most important lime-contributors 

 to the coral reefs, far more important than the corals themselves. 

 This has been found to be the case in Funafuti reef (Finckh), the 

 Fiji reefs (Gardiner), the Chagos group (Gardiner), etc. In all 

 these, animal, especially coral hfe.is relatively unimportant, while 

 plant life (nulHpores) Nourishes luxuriantly. (See the photograph 

 of a Lithothamnion reef in Nature, Vol. LXXII, pp. 571, 572.) 



In Bermuda, too, corals play a subordinate part in the reef 

 formation, Lithothamnion taking its place among the principal reef 

 builders (Agassiz-3). Nullipores also grow on the Challenger Bank, 

 raising the surface from considerable depths to within the zones of 

 coral growth. (Howe-24.) 



Lime-Secreting Alg.e of Fresh Water. These are chiefly 

 represented by Chlorophyceae of the family of the Stoneworts or 

 Cliaracccv, and they are widely distributed in the fresh-water lakes 

 of the temperate regions, and form extensive deposits of marl. 

 Analyses of Chara from the fresh-water lakes of Michigan showed 

 that something over 0.61 gram of soluble mineral matter occurs in 

 an average plant. This mineral matter is nearly 94% CaCOg and 

 is deposited as an encrustation on the outside of the plant. This 

 encrustation renders the stems and branches of the alga almost 

 white, and very brittle. On the average from 50 to 80 plants were 

 found on a square decimeter of lake bottom. Extensive beds of 

 marl or bog lime have in this manner accumulated at the bottoms 

 of ponds and small lakes. (Davis-14.) Marl beds composed 

 chiefly of the remains of Chara Jiispida have been found in various 

 parts of Scotland and elsewhere. Extensive deposits of "Characege- 

 lime" have been formed in the lakes of Denmark by the growth of 

 Chara. (Wesenberg-Lund-56:/55-75(5.) Such deposits are also 

 known among the older rocks. The organs of fructification of the 

 Charace?e sometimes accumulate in such quantities as to form parts 

 of extensive beds of limestones in both recent and earlier forma- 

 tions. 



In the Devonic of Ohio, and in other formations, occur lime- 

 stones often to a large extent composed of small spherical and 

 fluted bodies described under the name of Calcispliccra robusta Wil- 

 liams. These have also been regarded as the organs of fructifica- 

 tion of one of the Characese. 



. Fossil Phvtoliths of Algous Origin. 



Fossil OoLriKS. These occur in all geological horizons either 

 as autochthonous or as allochlhonous deposits. The latter generally 



