Anchor Ice 



83 



does not freeze in the current because of its motion, 

 but it does freeze on the bottom where the current 

 is sufficiently retarded to allow it. It congeals in 

 semi-solid or more or less flocculent masses which, when 

 attached to the stones of the bed, often buoy them up 



Fig. 24. A brook in winter. Country Club woods, Ithaca, N. Y. 

 Photo by John T. Needham. 



and cause them to be carried away. Thus the organ- 

 isms that dwell in the stream bed are deprived of their 

 shelter and exposed to new perils. 



Below the frost-line, however, in streams where 

 dangers of mechanical injuries such as above men- 

 tioned are absent, milder moods prevail. In the bed 

 of a gentle meandering streamlet like that shown in the 

 accompanying figure, life doubtless runs on in winter 



