[BARNES] TEMPERATURE OF RIVER WATER 43 



taken as a current at the freezing point with water around slightly above, 

 for he says that the river is cooled nearly to congelation. 



It needs actual experimental data, however, to state definitely that 

 colder currents do exist, especially when it has been demonstrated that 

 the currents under the ice do not differ by one hundredth of a degree 

 from freezing throughout the winter. It seems as yet no clear idea has 

 been held in legard to the difference between frazil and anchor ice. Some 

 observers hold that they are identical, while others that they are of 

 entirel}^ different origin. 



From a careful consideration of the data furnished in Mr. Henshaw's 

 paper, it seems to the, writer that the difference is largely a matter of 

 condition. From the very diverse ways in which ground ice is found, an 

 abundant supply 'of facts has been obtainable to support theories, with- 

 out sufficient regard being paid to the forces underlying the formation of 

 ground ice. 



Anchor-ice is formed on the bed of a river with the water at 32° F. 

 in proportion, as the depth of the river permits of radiation. Any agency 

 that could act as a check to radiation, as surface ice, would serve as a 

 preventive to the formation of ground ice. 



How far a mass of frazil crystals has been taken for ground ice, by 

 its formation at a depth and being held down by currents, is ditficult to 

 say. 



The ground ice found in the St. Lawrence Eiver, near the C. P. E. 

 bridge, at Lachine, has the appearance of frazil crystals. It is conceivable 

 that the first layers of ground ice, formed by radiation, when the river 

 was clear, could grow in thickness by the lower layers of frazil in the 

 water becoming fastened to them. 



Mr. Petex'son, referring to this ice on the bottom, near the bridge, in 

 the discussion following Mr. Henshaw's paper, states that, in taking 

 soundings in depths of water, varying from live to forty feet, the bottom 

 was frequently covered over its entire area with ice from two to three 

 feet in thickness. The sounding rod was sustained by the crystals, but 

 could be shoved through without much difficult}'. He further slates that 

 these crystals were formed during the entire winter, whenever there was 

 a period of intense cold, but whenever a period of mild weather followed, 

 these masses became detached, and, rising to the surface, were carried 

 down by the current. 



In regard to the relation between the depth of water, and the for- 

 mation of anchor-ice, Mr. Keefer states that ice forms on the bottom to a 

 dejjth of 40 feet, and that this depth is, to use his own words, '• in direct 

 " proportion to the descent of the mercury and the duration of that 

 " descent." 



It seems hardly possible to attribute ground ice to any other cause 

 but radiation. As radiation, however, is only dependent on the clearness 



