25J: RODDY— CONCRETIONS IN STREAMS. [May 7, 



ture and arrangement of the limy matter giving a decided though 

 rough coralline appearance to the inside portion and a more com- 

 pact texture to the outer part. The theory just given has been con- 

 firmed by a study of the distribution of the algse on the concretion- 

 ary bodies through the seasons. The fact also that when the limy 

 matter is dissolved out with acids, a mat of vegetable chains and 

 cells remains nearly as large as the original concretion is also con- 

 firmatory. Even in the concretions which are centuries old as 

 those in the forest covered deposit in Kendig's Woods the dead cells 

 and chains of blue green algae may be found. 



(3) Lime secreting algse are found in the Little Conestoga dur- 

 ing the entire year but abound from May till December. They 

 occur not only in the water but encrust many objects, in a few 

 places forming small reef-like accumulations similar to those in 

 Round Lake, New York. 



(4) Quite an array of investigators, among whom we may men- 

 tion Agassiz, Bigelow, Gardiner, Murray, Finckle, Vaughan, Wal- 

 ther. Drew, Matson, Dall, and Sanford, have studied at first hand 

 the activities of algae of the genera Lithothaninion and Halimeda 

 and also some of the bacteria in various parts of the ocean and in 

 many seas. All have come to the conclusion that many of the so- 

 called coral reefs owe their existence partly and often largely to the 

 activities of these lowly plants. The Bermudas, the Bahamas, the 

 Laccadive and Maldive Archipelagoes, Funafuti, and extensive 

 rock beds in the Floridian Peninsula have all originated through 

 plant agency as much as through coral polyps. If this be true, it 

 is not only possible but probable that fresh water blue green algae 

 throughout all the ages have caused and are still causing the precipi- 

 tation of rock materials from minerals in solution in streams and 

 fresh water lakes. 



(5) Weed has proved that the concretions formed in geyser 

 basins and known as Geyserites are formed by algae which through 

 life processes cause the precipitation of the siliceous matter held in 

 solution in the hot water. 



(6) The observation that the laminar accretion seems to pro- 

 ceed more rapidly on the under side of a concretion proves that the 

 formations are not due to mechanical precipitation of lime carbonate 



