PHYSICAL AND CLIMATAL CONDITIONS. 131 



it is enabled, by means of its less specific gravity, to 

 break away with a frozen layer of mud or sand attached 

 to it. It reaches the surface of the water with a bound, 

 and is instantly swept away by the incoming tide. The 

 spectacle thus presented by an extensive sand-bar after a 

 few hours of freezing weather, is most extraordinary; 

 the whole surface of the flood or ebb becomes suddenly 

 alive with blocks of ice, springing up from below, each 

 carrying away its burden of sand or mud frozen to its 

 base. Later in the season, towards the middle of March, 

 this singular phenomenon can be seen to the best advantage, 

 and it is curious to watch a block of, say, ten feet square 

 by five or six in thickness, being gradually covered by the 

 tide until it becomes lost to view for an hour or more, 

 during which time the water may have risen three or four 

 feet above it. ' When least expected ' up the submerged 

 mass springs ; it has broken loose from the frozen bottom, 

 it seems to stagger and pause for a few moments at the 

 surface, and then joins the rest of the icy stream on their 

 monotonous journey, until it is again stranded on some 

 other flat or bar during the ebbing tide. But this is only 

 a small part of the history of these ice-blocks, for, during 

 neap tides, it often happens that a block is stranded in 

 such shallow water that the flood has not power to raise 

 it from the substratum to which it is frozen. The block 

 grows there with every tide ; fresh films of ice and tidal 

 mud form all round it four times during every twenty- 

 four hours. It receives accessions from falling snows, and, 

 by the time the spring tides begin, it has greatly increased 

 in size and is more firmly frozen or weighted to the sand- 

 bar. Even the spring tides may not have the power to 

 free it from its icy bonds if the weather has been 

 extremely cold ; the consequence is that it goes on 



