176 NOTES ON ANCHOR ICE. 



by its rising and covering the surface) occurs only after several days 

 of a temperature considerably below zero. 



It also appears that anchor ice does not melt as readily as solid ice, 

 because it is found in banks under the field ice, during the v?hole 

 winter, even after the current has cut through the surface ice ; and in 

 the rapids where it has grown above the surface of the water, or 

 encroached upon the sides of the channel so as to dam back and raise 

 the water, it appears to yield upon the advent of milder weather 

 chiefly by losing its hold upon the bottom, and then only to the main 

 body of the current the lateral spread of which is disputed, inch by 

 inch, by this saturated " snow-ice." 



This ice is drawn into mill-races at the head of rapids wherever 

 there is too much current, or a lack of depth, and coming down to the 

 racks is sucked against the grating, completely stopping the water like 

 so much wool. At tail-races, where the same faults of construction 

 exist, it "grows" upon the bottom, setting back the water and stop- 

 ping the wheels. Many mills are rendered useless during the winter 

 months from one or both of these causes. 



Although a sounding pole will pass readily through a bank of 

 anchor ice, it cannot be easily penetrated or displaced by bodies 

 having any considerable base. In order to sink a crib for a bridge 

 pier, below one of the rapids in the Little River, the site was cut out 

 upon the surface ice, the crib framed in its place and filled with 

 stones ; after sinking a certain distance its progress was arrested, — 

 although the sounding pole shewed that it was still about ten feet 

 above the bed of the river. No additional weight which could con- 

 veniently be placed upon it would force it any lower, for it was found 

 to be resting upon a bank of "frozee" {frasil,fr.) or anchor ice. 

 The obstruction was only got rid of by the tedious process of detach- 

 ing, by means of long poles, small pieces at a time from the lower side, 

 which floated down the stream. 



In the little which has been written upon the subject of anchor ice, 

 it bas been doubted both that it is formed upon the bottom, and that 

 ice so formed rises to the surface ; or whether the anchor ice seen 

 upon the surface, was either formed or had rested upon the bottom. 

 Among practical men, millwrights and lumbermen who have been 

 puzzled by the phenomena attendant upon it, there is similar diversity 

 of opinion. It has, however, been observed in situations where it 



