252 RODDY— CONCRETIONS IN STREAMS. [May 7, 



ered a purely chemical problem, a solution of which may be looked for in 

 the action upon the bicarbonates of the oxygen set free by the plants. Of 

 these calcium bicarbonate is the most abundant, and the reaction upon it may 

 be taken as typical and expressed by the folllowing chemical equation, 

 CaH2( 003)2 + O -^ H.0 + CaCOs + CO2 + O, in which the calcium bi- 

 carbonate is converted into the normal carbonate by the oxygen liberated by 

 the plants and both carbon dioxide and oxygen set free, the free oxygen 

 possibly acting still further to precipitate more calcium monocarbonate, 

 CaCOs." 



Dr. F. W. Clarke in "Data of Geochemistry" says: 



" That Dr. Davis' theoretical equation (given above) rests on no ex- 

 perimental basis." 



In an article in Science dated December 14, 1914, J. Claude 

 Jones, of the University of Nevada, says that the tufas of Salton 

 Sea and of Pyramid Lake owe their origin to blue green algse. He 

 .shows that wherever these plants are present in Pyramid Lake the 

 gravels are cemented together and wherever the algae are absent 

 no trace of the tufas can be found. 



Dr. Clarke ascribes the origin of the " Water Biscuits " of Lake 

 Canandaigua to the same agency. 



Miss Josephine Tilden in Minnesota Algce (1910) says that 

 Gleocapsa calcarea forms a calcareous crust (with other lime secret- 

 ing forms) on boards where spring water from a trough drips down 

 constantly. 



Weed in his classic report (1889, U. S. G. S.) on the rock for- 

 mations of the hot springs of the Yellowstone National Park shows 

 that travertine as well as siHceous sinter are deposited through the 

 aid of algse. 



Dr. B. M. Davis, of the University of Pennsylvania in a very 

 interesting paper {Science, Vol. VL, July 30, 1897) describes the 

 algse and bacteria active in the formation of the travertine and 

 siliceous sinter deposits in Yellowstone Park. 



Dr. MacFarlane, of the University of Pennsylvania, in speaking 

 of the activities of thermophilic algse of hot spring and geyser 

 regions, ascribes many rock formations throughout the earth's his- 

 tory as due to the work of fresh water algse especially of the group 

 Cyanophycess. 



