1901.] in the Rivers of Upper Burma. 61 



particles of carbonate of lime could be retained, if the pi'ocess of deposi- 

 tion were merely mechanical. The growing surface of the deposit is 

 always covered with a growth of bright green algaj and it is well- 

 known that chloi'ophyll bearing algae have the power, under the 

 influence of light, of directly assimilating the carbon contained in 

 carbonic acid. It seems probable therefore that these aigas which 

 naturally grow most rapidly in position where there is a considerable 

 rush of water, bringing an abundance of their natural food, assist in the 

 deposition of the carbonate of lime by destroying the carbonic acid 

 which holds it in solution ; while the felted mass of fibrous alga3 

 affords a means of retaining the minute particles of calcite and allowing 

 them to grow together into the granular crystalline deposit of which 

 the dams are built up. 



