210 THE LABRADOR PENINSULA. chap, xxxiv. 



is very probable that this form of ice lias been instru- 

 mental in producing great changes in the valleys of 

 northern rivers. 



lowest summer level has, at tlie taking or departure of the ice, sometimes 



attained a maximum of twenty-five feet In the latter part of 



January 1857, after a cold ' term ' of unexampled severity and duration — 

 long after the ice had taken, opposite the city, and when, according to all 

 previous experience, no further rise was to be apprehended, either above or 

 below the rapids, until the ' break-up ' in the spring — the river, above the 

 Lachine Rapids (where it is always imfrozen), rose suddenly four to five feet, 

 pouring an Arctic current down the aqueduct of the new water- works. A 

 few feet more of elevation would have sent the river over its banks, and the 

 consequences might have been most serious. 



Such intense cold was followed, as is usual, by a rapid rise of temperature, 

 whereupon the water fell about two feet, bat thereafter remained for weeks 

 at least two feet above its ordinary level. 



There is a tradition of something similar having occurred about seventy 

 years ago, but this was not heard of until after the irruption ; all recent ex- 

 perience and enquiry going to show that, after the ice has taken, the water in 

 this reach lowers gradually with slight fluctuations until the spring. 



This flushing above the rapids was independent of any movement of the 

 fixed ice below, either opposite Montreal or in the Laprairie Basin, the 

 levels of which remained imdisturbed. Another peculiai'ity was the absence 

 of any visible cause ; no ice had descended, or was descending, and on the 

 surface nothing but blue water was to be seen. The continuous descent 

 (for days and weeks before the river is frozen over above the city) of large 

 masses of ice, which being arrested below would dam back the water, is 

 sufficient to account for the rise at Montreal ; but in this case there was no 

 descending ice, the Lake St. Lotus 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 deposition of 

 ' anchor ' or ' ground ' ice upon its rocky and stony 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 foimd in banks 

 under the solid ice below rapids or currents of open water. In consequence 

 of the difliculty 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. Lawrence, wherever there is open water. 



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



