LOGAN ON THE PACKING OF ICE IN THE ST. LAWRENCE. 423 



from Longeuil on the opposite shore. In the narrow channel be- 

 tween them, the water, rushing with much force, produces the 

 Sault Normandy and cooped up a little lower down by the island of 

 St. Helen and several projecting patches of trap, it forms St. Mary's 

 Current. 



The interval between St. Helen and the south shore is gi:eater 

 than that between it and Montreal ; but the former is so floored and 

 crossed by hard trap rocks that the St. Lawrence has as yet produced 

 but little effect in wearing them down, while in the latter it has cut 

 out a channel between thirty and forty feet deep, through which the 

 chief part of its waters rush with a velocity equal to six miles per 

 hour. It is computed that by this channel alone upwards of a mil- 

 lion of tons flow past the town every minute. 



Between this point and Lake St. Peter, about fifty miles down, 

 the river has an average breadth of two miles, and proceeding in 

 its course with a moderate current, accelerated or retarded a little 

 according to the presence or absence of shoals, it enters the lake by 

 a multitude of channels cut through its delta, and forming a group 

 of low flat alluvial islands. 



The frosts commence about the end of November, and a margin 

 of ice of some strength soon forms along the shores of the river and 

 around every island and projecting rock in it; and wherever there 

 is still water it is immediately cased over. The wind, acting on this 

 glacial fringe, breaks off portions in various parts, and these pro- 

 ceeding down the stream constitute a moving border on the outside 

 of the stationary one, which, as the intensity of the cold increases, is 

 continually augmented by the adherence of the ice-sheets which 

 have been coasting along it; and as the stationary border thus robs 

 the moving one, this still further outflanks the other, until in some 

 part the margins from the opposite shores nearly meeting, the float- 

 ing ice becomes jammed up between them, and a night of severe 

 frost forms a bridge across the river. The first ice -bridge below 

 Montreal is usually formed at the entrance of the river into Lake 

 St. Peter, where the many channels into which the stream is split 

 up greatly assist the process. 



As soon as this winter barrier is thrown across (generally towards 

 Christinas) it of course rapidly increases by stopping the progress 

 of the downward-floating ice, which has by this time assumed a 

 character of considerable grandeur, nearly the whole surface of the 

 stream being covered with it; and the quantity is so great, that to 

 account for the supply, many, unsatisfied with the supposition of a 

 marginal origin, have recourse to the hypothesis that a very large 

 portion is formed on and derived from the bottom of the river, where 

 rapid currents exist. Butwiiatever its origin, it now moves in solid 

 and exteuiiive fields, and wherever it uhhHs with an obstacle in its 

 course, the momentum of the mass breaks up the striking part into 

 huge fragments that pile over one another; or if the obstacle be 

 stationary ice, the fragments are driven under it and there closely 

 packed. Beneath the constantly vvidening ice-barrier mentioned, 

 an enormous quantity is thus driven, particularly when the barrier 



