POLAR ICE.- — DIFFERENT KINDS. 227 



sisting of roundish nodules, and fragments of ice, 

 broken off by the attrition of one piece against an- 

 other. This may be considered as the wreck of 

 other kinds of ice. 



6. Bay-ice is that which is newly formed on the 

 sea, and consists of two kinds, common bay-ice, and 

 pancake-ice ; the former occurring in smooth exten- 

 sive sheets, and the latter in small circular pieces 

 with raised edges. 



7. Sludge consists of a stratum of detached ice- 

 crystals, or of snow, or of the smaller fragments of 

 brash-ice floating on tiie surface of the sea. This 

 generally forms the rudiments of ice, when the sea 

 is in agitation. 



8. A hummock is a protuberance raised upon any 

 plane of ice above the common level. It is frequent- 

 ly produced by pressure, where one piece is squeezed 

 upon another, often set upon its edge, and in that 

 position cemented by the frost. Hummocks arc 

 likewise formed, by pieces of ice mutually crushing 

 each otlier, the wreck being heaped upon one or 

 both of them. To hummocks, principally, the ice 

 is indebted for its variety of fanciful shapes, and its 

 picturesque appearance. They occur in great num- 

 bers in heavy packs, on the edges and occasionally 

 in the middle of fields and floes, where they often 

 attain the height of thirty feet or upwards. 



9. A calf is a portion of ice which has been de~ 

 pressed by the same means as a hummock is ele- 



u 2 



