NOTES ON ANCHOR ICE. t7S 



being frozen over just above Lachine, and the narrow bordages, in the 

 intervening distance of about four miles to the rapids, remaining in 

 situ. What then caused this mysterious and alarming elevation of 

 the river in the dead of winter when there had been no rain or 

 thaw, and while all its tributaries were sealed by intense frost ? 



The St. Lawrence was undoubtedly raised in its bed by the deposi- 

 tion of " anchor" or "ground" ice upon its rocky and stony bottom. 



"While the weather continues cold, no matter how intense that cold 

 may be, nothing but a surface of clear water is visible in that stretch 

 of rapid river between the Lachine Rapids and Lake St. Louis ; but 

 upon the first mild day after very cold weather, the whole surface of 

 this open water is covered with white-capped cakes and floes of 

 "sludge" or "brash" ice, which continue to descend for a day or 

 two, when all is clear again. By watching the river closely, changes 

 will be observed in the number and form of the ice-cakes in any given 

 area : this is caused by new accessions which rise above the surface 

 with a slight spring, a dark-coloured mass like snow saturated with 

 water, but which rolling round and settling back speedily assume a 

 snow- white cap — by the drainage of those parts above the water level. 



This spongy ice which has thus left its anchorage is carried down 

 the river and stowed away under the field ice, — upon the shoals and 

 in every nook and crevice where the current is weak, — and is also 

 tucked by the eddies under the bordages until it rests upon the 

 bottom. 



Anchor ice is formed only in open-running water. It never forms 

 where the surface is covered with stationary ice, although it is often 

 found in banks under the solid ice below rapids or currents of open 

 water. In consequence of the difficulty and danger of sounding in 

 such situations, and in such severe weather, the limit to the depth of 

 water under which it will form is not easily ascertained : but there is 

 no reason to doubt that it forms upon the whole bed of the St. Law- 

 rence, wherever there is open water. 



It does not appear that great or continued cold is necessary to its 

 formation in all situations, as it has been found in brooks immedi- 

 ately after the first frost and before lake ice has become safe for 

 travel : it is also one of the earliest formations upon those portions of 

 shoals and rapids barely covered with water. But in the deeper 

 water above the head of rapids its abundant formation (as indicated 



