278 Field a?id Forest Rambles. 



Mexico ; at all events, the same phenomenon is remarked at 

 least over the north-eastern portion of the continent. The 

 influence of warm winds in spring on the melting of the snow 

 is remarkable. A sudden change from the north to south or 

 west will raise the thermometer some forty degrees in the 

 course of a^ few hours, when the thick mantle of snow seems to 

 vanish as if by an enchanter's wand. Indeed the warm air 

 currents appear to have a greater influence than rain on the 

 vast accumulations of snow in the forests. Such rapid tran- 

 sitions of temperature occurring during the Glacial epoch 

 would have flooded the valleys, and on the grand scale con- 

 sequent on the arctic climate of the time, must have been 

 equal to produce the vast gravel and river valley accumula- 

 tions seen everywhere throughout the length and breadth of 

 this region. 



With reference to the interesting and suggestive appearances 

 already detailed in connection with the breaking up of the ice 

 in the Canadian rivers, which, although on a small scale as 

 compared with past epochs, is of great importance to the 

 geologist when speculating on the conditions in connection 

 with Glacial and post-Glacial epochs ; we have seen the effects 

 of sudden thaws in damming back the rivers and inundating the 

 intervals, or " carse lands " as they would be called in Scotland. 

 Moreover, the pressure of these ice-floes furrows and tears up 

 the river's banks, whilst masses form in shallow places and 

 pick up pebbles and debris from the bottom, and deposit them 

 wherever the bergs melt, often far below the places where they 

 were first soldered by the icy matrix. The accumulated im- 

 petus gained by the crowding of the bergs as they float along 

 must be enormous, carrying off trees, dwellings, or whatever 

 obstacles impede the onward progress of the floating chaos. 



Many stately pines and birches growing on the banks of the 

 St. John, were pointed out to me, showing, by being nearly 

 bent double, how the force had pressed on them. I recollect 



